How can I stop my toes from going numb on long rides? I've begun trying to commute to work, which is a 70+ minute ride each way for me.  I find that after about 30 minutes of riding, my toes in both feet begin to go numb.  It's not a cold thing, because it happens in warm weather too.  It's more of a pins-and-needles, limb going to sleep feeling, though it hits all my toes and sometimes a little further into my foot (never really past the ball though).  

This happened with my old flat pedals and several different pairs of shoes.  I recently switched to clipless pedals and shoes and hoped it would stop with the stiffer sole and dedicated contact to the pedal, but no dice.  My cycling shoes are quite comfortable and there is no pain associated with this, just the annoying numbness.  Right now the only way I can fix it is to coast for a while so I can unclip and dangle/shake my foot around to get some feeling back into it.  Unclipping and temporarily pedaling with my heel helps a little, but not much.

Anybody else have this problem or know how to alleviate it?  Or am I just stuck with it due to some quirk in my anatomy?
There is probably a combination of things that can help.  Periodically getting your weight off can help as can making sure your pedaling stroke includes ankle flexion.  In my experience, that helps a lot with circulation in my feet.  Obviously, you'll want to make sure your shoes are not laced or velcro-ed too tight.  I will often stand in the pedals and do calf stretches by flexing my ankles up and down (still clipped in) to help with foot circulation.