If you've got phantom power on your machine & large diaphragm phantom powered mics then you don't need a pre-amp. Start with the Behringer B1 which is a doozy all-rounder for the price. Otherwise, you just need to keep playing with it until the results inspire a warm glow in your ego.

What have you got anyway? I'm presently using a Fostex MR8-HD, though I recently tried the Kord D-888 but there's a design flaw when it comes to using phantom power. I've also been looking at the Alesis iMultiMix 8 which does away with internal hard-drive and records on an i-Pod. The Zoom R16 uses flash-cards, but only two of the xlr inputs are phantom powered, which necessitates a mixer.