Depending on what your needs are, and if you're going to be mic'ing the drums and bass, you might need a couple of sub's and a crossover. You might also was a 2 channel Eq. One side for mains (FOH) and the other side for the stage monitors. They can help reduce feedback and adjust the system for whatever type of venue you're playing at. A good 8-12 space rack for the amps, crossover, eq, etc... would be nice too.
It's alway's better to have more power and volume than you'll actually need.