There is no magic number or sets or reps, really what it all boils down to is picking a scheme that works for you and that you can progress on. As long as you are either adding a little bit of weight or cranking out an extra rep or two each week then you are doing something right, if not you need to rethink things.
For your reference here are the basic rep purposes:
1-3 pure strength
5-7 power
8-12 hypertrophy
15+ endurance
A lot of strength coaches like 5 reps, cause it fits the bill for both strength and mass gains. For bodybuilding, generally 6-8 for heavy work is good, with occassional low rep work for pure strength. Personally I vary my ranges for different exercises but like 5-8 for the big lifts, and 8-12 for isolations.