It totally depends on what kind of training you are doing.
If you are doing low volume/heavy lifting in the range of 3-6 reps per set, likely your going to wait minutes between sets.
If you are doing a higher volume/lighter lifting routine, then typically I'd wait between 40seconds to a minute (no more).
Of course you can temper that with "what are you trying to achieve in the first place?"
Higher volume low weight routines do in fact have a cardio/fat burning aspect to them. While not as tailored to most of the folks on this board and thier goals, they do have some validity if done correctly. One of the "correct" aspects is the shorter rest time for these routines.
Generally, the reverse can be seen as true for the low vol/high weight routines.