The male refractory period is simply the recuperative or restorative time required between orgasms. This has been a topic off and on in the Peak Testosterone Forum. Most men remember when they were younger and could orgasm many times during a 24 hour period. Suddenly, though, they find themselves in middle or senior age sometimes not able to orgasm at all for 24 hours or more! This can be very distressing since even no erections come during this time by definition.
Look at what this man wrote in a thread he entitled "My Arousal System is Not Working:"
"Please help I am quite a horny person , have lots of libido and desire but not the ability . I have a poor refractory period too so this is quite frustrating. I have decided to change this situation as its making my life unhappy and complicated My new girlfriend is quite understanding but not sure how long for,as i sense frustration burning inside her.... I have lots of desire and libido but poor inadequate erections. Help please." 
Many people exlain this increase in refractory period by "aging". This is certainly true to a certain degree, but I would argue that most of the time an overly increased refractory period is a sign of an underlying medical condition or lifestyle issue that needs to be addressed. Below we will look at several common causes of an inflated refractory period and how you can address them:
1. Nitric Oxide. There are indications that nitric oxide plays a powerful role in recovery from the refractory period. The reason is that some of the PDE5 inhibitors (Viagra and Levitra specifically) have significantly reduced the refractory period in younger, relatively healthy males. One study found that "sildenafil administration led to a marked reduction of the post-ejaculatory refractory time (10.8 0.9 min versus 2.6 0.7 min for placebo and sildenafil respectively; P < 0.0001). These results indicate that in normal subjects acute sildenafil treatment does not modify semen characteristics and has a positive influence over the resumption of erections following ejaculation in the presence of a continuous erotic stimulus."  Similar results were found in men with actual premature ejaculation. 
In fact, PDE5 inhibitors have even been used to treat premature ejaculation for the simple reason that it helps young men with premature ejaculation to be ready for a second orgasm more quickly and thus builds their confidence in the bedroom.  This approach should be viewed with caution for all the reasons I outline in My Links on PDE5 Inhibitors.
Now it would be nice if they would have studied this in middle-aged or senior men, but such is not the case as far as I know. However, anecdotally many men have noticed the accelerated recovery time after Cialis in particular. This could be from a number of different factors, but one of them is likely the increased nitric oxide.
My site is packed, by the way, with ways to increase nitric oxide. Look through these links on Improving Erectile Strenght for literally dozens of ideas.
2. Prolactin and Dopamine. Prolactin and Dopamine provide a yin and yang effect on each other and both can play a signifcant role in the refractory period. Elevated levels of prolactin, for example, will lower both testosterone and libido, something I document in my link on Testosterone and Prolactin. More to the subject, excess prolactin will also raise your refractory period significantly. Furthermore, one study of cabergoline, which lowers prolactin levels, showed significant improvements in the refractory period in ten healthy males. 
Of course, that is particularly interesting, because no one would be suprised if good results were obtained in men with a prolactinoma or high prolactin levels. However, cabergoline helped even normal men reduce their refractory period, indicating that prolactin reduction probably applies across the spectrum.
Why does prolactin affect the refractory period? Well, dopamine actually inhibts prolactin at the pituitary. So dopamine clearly plays a role in the refractory period as well, and this has been shown in animals studies.  Now what is interesting is that recent research has shown that both overly high and overly low dopamine levels can raise prolactin. 
What can cause dopamine problems. Dopamine dysregulation can occur, ironically, from sleep deprivation. See my link on Sleep and Erectile Dysfunction for more details. Use of you-know-what has been shown to dull dopamine receptors.  And, finally, if you need to raise dopamine levels, you may want to see my link on Natural Dopamine Increasers.
What about natural ways to lower prolactin without having to resort to cabergoline, which is rife with side effects? Well, on the forum both Vitamin B6 and mucuna pruriens have been touted for their natural prolactin lowering effects.  As always, I recommend talking to your doctor first before trying any new supplement.
3. Nerve Sensitivity. This is pretty obvious, but almost anything that will improve penile sensitivity will likely help the refractory period. The nerve involed here is the dorsal nerve of the penis and researchers have (one could argue rather cruelly) removed half the nerve fibers from the dorsal penile nerve in monkeys and found - lo and behold - that the refractory period increased significantly.  This same study found that "the refractory state after ejaculation in the human male is accompanied by an increased PST, and a state of hypoexcitability and hyposensitivity." By PST, the authors were referring to the "Penile Sensory Threshold", which was higher after an orgasm.
Basically, an orgasm "exhausts" your nerves in the area and raises the threshold for you to get excited and stimulated. Okay, so may it didn't warrant a million dollar study to come to that conclusion, but it does allow us to focus on something important: healing any neuropathy or pre-neuropathy that we might be experiencing. Many men, especially diabetics, begin to experience a decline nerve sensitive in their limbs and extremeties. And, yes, that can mean the penis is affected. For natural solutions - of course, check with your doctor first - see this link on Neuropathy Remedies. And, of course, get your blood sugar and insulin parameters tested, including such tests as fasting blood glucose, fasting insulin, A1C and triglycerides.
4) Seratonin. SSRI's for depression are a major source of sexual dysfunction. This occurs for a number of reasons, but one of the less known ones is the fact that seratonin plays a role in the male refractory period. One animal study looked at multiple ways to lower seratonin and found that they all decreased the refractory period. Thus, both dopamine AND seratonin seem to play a significant role in post-orgasmic recovery. 
5) Low Testosterone. Many of you hypogonadal men out there reading this will not at all be suprised to learn that low testosterone has been found in a couple of studies to lead to an increased refractory period.  So, if you can afford it, this is yet another reason to ask your doctor about getting your T checked. My guess is that high estradiol would do the same, although I do not have a study to prove that yet. But, generally, high estradiol sexual symptoms are identical to that of low testosterone.
2) Hum. Reprod, 2000, 15(1):131-134., "Effects of sildenafil (Viagra ) administration on seminal parameters and post-ejaculatory refractory time in normal males*"
3) BJU International, Apr 2011, 107(8):1274 1277, April 2011"The effects of three phosphodiesterase type 5 inhibitors on ejaculation latency time in lifelong premature ejaculators: a double-blind laboratory setting study"
4) The Journal of Sexual Medicine, May 2005, 2(3):368 375, "Efficacy of Sildenafil Citrate (Viagra) in Men with Premature Ejaculation"
5) BJU International, Jun 2000, 85(9):1093 1096, "The postejaculatory refractory period: a neurophysiological study in the human male"
6) J Endocrinol, 2003 Dec, 179(3):357-65, "Effects of acute prolactin manipulation on sexual drive and function in males"
7) Eur J Endocrinol, 1999 Oct, 141(4):387-95, "Dopamine agonists both stimulate and inhibit prolactin release in GH4ZR7 cells"
9) Behav Brain Res, 1984 Jun, 12(3):267-73, "Brain monoaminergic control of male reproductive behavior. II. Dopamine and the post-ejaculatory refractory period"
11) N Engl J Med, 1979 Jan 18, 300(3):141-2, "Dangers of vitamin B6 in nursing mothers"
12) Clinical Endocrinology, oct 2005, 63(4):381 394, "Effects of testosterone on sexual function in men: results of a meta-analysis"
14) Behavioural Brain Research, Jun 1984, 12(3):255 265, "Brain monoaminergic control of male reproductive behavior. I. Serotonin and the post-ejaculatory refractory period"