This site emphasizes natural health practices that can supercharge a man's life (and sex life). Of course, exercise and a clean, whole foods diet are probably the top two items that come to mind. But right behind those should be Secular Meditation in its various forms. (I would also throw Progressive Muscle Relaxation into the mix as well due to its profound benefits.) Meditation may not seem manly, but, when you look at the benefits, it is hard to beat and I will prove that below when we examine Mindfulness Meditation specifically.
One of the myths that we have is that you always have to work harder to get ahead as a guy. Mindfulness Meditation shows how just untrue that assertion is: it shows that by just sitting quiety for 1 or 2 10-15 minutes periods during your day you can rebuild your body, brain, personal psychology and hormones. Again, "work smarter, not harder" applies perfectly here.
Here are a few of the stunning benefits for men of Mindfulness Meditation:
1. Brain Building for Career and Relationships. Several studies have noted Mindfulness Meditation's ability to rebuild many parts of the human brain. For example, one study found that it took just a few months to see increased "left anterior" brain activation.  This echoed a previous study on particpants with SAD (Social Anxiety Disorder), who were not only helped with their people-related issues but also saw increased activity in areas of the brain used for focus and attention.  And in those with mild cognitive impairment, Mindfulness Meditation increased both the density of the hippocampus (memory) and the "inferior frontal gyrus".  However, it should be noted that one study showed improvement in the hippocampus in normal, healthy individuals. 
Now, just in case the importance of this escaped anyone, let me translate what this means:
The typical man in a modern, industrialized environment is stressed out with career, relationships, finances, commuting and the overstimulation of television, media and the internet. This type of man, though, is the ideal candidate to be helped from Mindfulness Meditation, since rebuilding one's brain is clearly going to be of great benefit for both career and relationships. Seriously, how can increasing the density of neuroconnections in your brain not be good for almost everything you do in life as a male?
Also, many men have lived lives of depression, post traumatic stress disorder and other major cortisol-increasing stressors that can actually shrink the brain. Now, thru this simple meditational technique, these men have been give the chance to rebuild their brains and recover much of those lost years. Again, though, it is not just the stressed that will benefit according to some of the evidence, but healthy, "normal" individuals as well.
NOTE: Interested in giving it a try? Consider reading my link on How to Do Secular Meditation, which gets rid of all the religious verbiage associated with meditation and distils it down to just the most simple steps.
2. Cortisol Reduction. Did you know that one study showed that cortisol levels did not change from the beginning of an Mindfulness session to the end.  Does this mean that it has no effect on cortisol? Actually, the same study showed that the longer one meditates, the lower the cortisol levels. And as you hopefully know from My Links on Cortisol, it is one of our most potent enemies.
There are many reasons that cortisol will rip your health and sex life apart, but the primary ones are probably a) accelerated visceral fat, which is associated with cardiovascular disease and endothelial, a.k.a erectile dysfunction, b) brain shrinkage and c) testosterone reduction. And overexcitation of the HPA Axis in general can lead to or accelerate many psychiatric disorders as well.
So anything that lowers cortisol and/or keeps it in check is a potent tool in your arsenal. And Mindfulness Meditation has lowered cortisol in a number of studies with a wide variety of patients.
3. Executive Function. There are few things more important to your career and relationships than executive function. Wiki definites executive function as "cognitive processes that regulate, control, and manage other cognitive processes."  It involves multitasking, reasoning, working memory and many, many other critical things that separate us from the rest of the animal kingdom. And poor executive executive function is associated with "attention deficit hyperactivity disorder, depression, drug abuse, and antisocial behavior." 
Mindfulness Meditation has been shown in several studies to be excellent at improving executive function in many key ways, including "increasing awareness of one's thoughts, emotions, and actions have been shown to improve specific aspects of EF, including attention, cognitive control, and emotion regulation."  Who can improve their executive function? Studlies look promising for just about everyone and include groups as diverse as and 2nd and 3rd graders. 
NOTE: Some of these studies are based on MBSR (Mindfulness Based Stress Reduction) which is mindfulness meditation plus some other things such as class instruction and yoga. Nevertheless, the core of all these programs is just pure Mindfulness Meditation.
4. High Blood Pressure (Hypertension). One of the biggest risk factors for erectile dysfunction and sexual dysfunction is high blood pressure. High blood pressure has many apsects to it. Everyone knows that narrowing of the arteries from arteriosclerosis can lead to high blood pressure and on this site we often discuss how endothelial damage from a Western lifestyle can lead to decreased nitric oxide and hypertension. However, for many men the primary component of their high blood pressure is stress-related Western lifestyle. This is where Mindfulness Meditation can really make a difference and lower blood pressure. Many studies have shown just this, including cancer pateints  and junior high students. 
5. Social Life. This is odd, but sitting quietly doing Mindfulness Meditation can improve your social life. As mentioned above, researchers found that people with Social Anxiety Disorder were greatly helped because their "stress reactivity" to social situations.  In other words, this type of meditation helps to keep you from overreacting and, again, this was also evidenced by decreased activity in the amygdala, the part of the brain involved in fear reactions.
6. Depression. The Peak Testosterone Forum is packed with men who are struggling or have recently struggled with depression. Many are on depression medications such as SSRI's. MBSR has been thoroughly studied as a treatment for depression and has done very well in the studies overall, showing benefits for a variety of patients including some of the tougher treatment groups such as cancer patients. 
Admittedly, not all studies have shown improvement from MBSR. However, another mindfulness approach called Mindfulness Based Cognitive Therapy (MBCT) has even been used very successfully even with patients who have experienced recurring bouts of major depression. One meta-analysis concluded that it prevented relapse into major depression at a very high rate.  The authors also noted that "in two studies, MBCT was at least as effective as maintenance antidepressant medication."
7. Amygdala (the Brain's Stress Region) Reduction. There are some areas of the brain that you don't want to build up. In fact, researchers have noted that a decrease in one area of the brain, the amygdala that is responsible for panic and fair, is actually a good thing. And, sure enough, Mindfulness Meditation shrinks this critical part of the brain, showing just how forcefully it reduces stress.  Another study noted the same shrinkage of the amygdala on "stressed but otherwise healthy" individuals, which covers just about everyone in modern, urban societies! 
8. Immunity. The same study that noted increased brain activity from meditation also found that meditators had a much better immune response against the influenza vaccine, thus likely providing very real protection against flus and other viruses. 
1) Psychosomatic Medicine, Jul/Aug 2003 vol. 65 no. 4 564-570, "Alterations in Brain and Immune Function Produced by Mindfulness Meditation"
2) Emotion, Feb 2010, 10(1):83-91, "Effects of mindfulness-based stress reduction (MBSR) on emotion regulation in social anxiety disorder"
3) Soc Cogn Affect Neurosci (2010) 5 (1): 11-17, "Stress reduction correlates with structural changes in the amygdala"
4) BMC Complement Altern Med, 2012, 12(Suppl 1):P202, "Mindfulness based stress reduction in adults with mild cognitive impairment: a pilot study using fMRI"
5) Psychiatry Research: Neuroimaging, Jan 2011, 191(1):36-43, Mindfulness practice leads to increases in regional brain gray matter density"
6) Neuropsychobiology, 65(3), "Influence of Mindfulness Practice on Cortisol and Sleep in Long-Term and Short-Term Meditators"
7) Behaviour Research and Therapy, Nov 2012, 50(11):651 660, "Improving sleep with mindfulness and acceptance: A metacognitive model of insomnia"
9) Brain, Behavior and Immunity, 2007, "One year pre post intervention follow-up of psychological, immune, endocrine and blood pressure outcomes of mindfulness-based stress reduction (MBSR) in breast and prostate cancer outpatients"
11) Child Development Perspectives, Article first published online: 21 JUN 2012, "Improving Executive Function and Its Neurobiological Mechanisms Through a Mindfulness-Based Intervention: Advances Within the Field of Developmental Neuroscience"
12) Journal of Applied School Psychology, 2010, 26:70 95, "Effects of Mindful Awareness Practices on Executive Functions in Elementary School Children"
13) Psychosomatic Medicine, Nov 1 2004, 66(6):909-914, "Impact of Meditation on Resting and Ambulatory Blood Pressure and Heart Rate in Youth"
14) Clinical Psychology Review, Aug 2011, 31(6):1032 1040, "The effect of mindfulness-based cognitive therapy for prevention of relapse in recurrent major depressive disorder: A systematic review and meta-analysis"