Like everyone else said, everyone has their own opinion....but what has worked really well for me is a training system by MD columnist - Eric Broser - called Power/Rep Range/Shock.
I would quickly describe it as a 3-distinctly different weeks that incoporates all types of training from Power (4-6 reps) to Rep Ranges (7-9, 10-12, 13-15 and even 16-20) to Shock (drop sets and supersets). Once you're done, start back with power week and do 3-4 cycles and you'll see results!
Google it and let me know what you think.