It depends on what you mean by "good sound". You may want something that is solid state (what goes in is what comes out) or you may want something that adds "color" or "distortion" to the signal going in (like a tube pre amp.)
At this point, I would focus on hardware instead of going the software route, but if you do go the software route, look into the MCDSP plugins and the URS plugins. If you are looking for some hardware thats going to depend on your budget, but the Really Nice Pre Amp is a good choice, and so is the aphex model that Youngmoe uses. Grace makes good pre amp in the $600 and under range also, and the presonus blue tube had 18 points out of 20 in Electronic Musician. No matter what, get the mic first and additional gear later.