You've got lots of advice! These clicks are very common in all bikes and the key point is to narrow it down.
Check to see if it is specific to one side. When I had a similar problem I managed to pedal a few metres with one leg at a time using the SPDs to pull up. This confirmed it was in the left pedal/crank. Start with the simple things, eg. grease and tighten pedals. If still a problem remove crank (when you are near a bike shop unless you have an extensive tool kit) and grease the square taper, also reposition and grease EBB as Fred suggests. There are varying opinions about greasing the cranks but I always do and have not had any problem. Next most likely are chain ring bolts which could be loose. If all else falls listen to your ipod on high volume!