Here's what I did, and began to see gains really quickly. Take a look at RJ's workout programs:
You don't need to do the entire program. If you have the time, I highly recommend them, but they're intensive and quite time consuming. I should note that I'm in the midst of the 12-week muscle building program and it's kicking my ass; in a good way. What I did to really get going from my plateau, however, was to look through certain parts of the workout routines, and certain exercises specifically, and replace what I was doing with that muscle group.
A good example, for me, is shoulders. There are TONS of different exercises you can do for your shoulders. Try some, then try some more. When you like the gains you get from one, do it until you get bored of it, then do another. Keep in mind, too, that the very first time you try a new exercise, you really need to make sure your form is correct, otherwise you won't "feel" it working. Incorrect form could also lead to injury. That's another factor to consider. Don't do a new exercise if it exacerbates an existing (or developing) injury. If it hurts, do something else. This is such a "duh" thing to say, but lots of my friends have hurt themselves because they just tried to power through.
I would also highly suggest supersets. There are great examples in RJ's programs. They keep your heart rate up and make your routine go faster.
That said, there are certain exercises I would never change, because they're just that good. Squats are a great example, same with bench press and flys. No matter what, I'll be doing those during leg/chest days.
Good luck, man!