well for AMD systems the thing to look for it the mounting bracket. Anything labeled with AM2/AM2+/AM3 should work because they use the use the same retention module. After that just pick a good cooler. Something with direct heatpipe seems to work well. Some of the fans will have PWM (Pulse Width Modulation I believe). Basically that is letting your motherboard regulate how fast your cpu fan should spin. This will be a 4 pin connection to your motherboard. 3 pin headers will spin at full rpm but usually they will come with some sort of fan controller. For the fan size, bigger fans = quieter and better cooling.
Hope that answered some of your questions.