What kind of mic do you have, because certain mics work better with certain preamps and certain mics are better are recording R&B than they are hip hop and vice versa? I personally use the Avalon 737sp and I can tell you it mkaes a world of difference. Plus the 737 has compression and eq on it so you got a hardware device to physically shape your recordings before you track them in pro tools. I use to use the focusrite VoiceMaster and Twin Trak mic pres(from the platinum series) and after really doing a lot of recording on them I finally got a pretty decent sound out of them, but the Avalon is plug and play, the more in depth you get with them the better the sound. My advice though is if you don't have some good monitors, get those and the focusrite stuff as opposes to dropping 2k on the avalon. I also hear Trident makes some excellent sounding mic preamps and I think one of them is about 1g.
Oh yea, converters make a world of difference too. Protools converters are decent but i'd try to get the Rosetta or any kind of apogee converter if possible, the difference in your recordings is night and day!