With regard to Pennywizz6's recommendation of the Lexicon Omega--make sure you check out the reviews at
http://www.musiciansfriend.com/srs7/fg=102/g=rec/product/reviews/base_pid=245505/rpp=10/

Lots of very positive feedback. I have the Mbox with Protools, a similar unit that costs more but has only 2 simultaneous inputs. (I believe the Omega allows 4 simultaneously.) The Lexicon version wasn't available when I bought mine or I probably would have gotten it instead. The Lexicon seems more like an all-in-one package as opposed to Protools, which forces you to buy expensive plug-ins to get good quality. I am not all happy with the effects and compression that come standard with the Mbox. While I do not have the Lexicon Omega, I can tell you that based on my experience with my PCM 80 and 90 reverb and delay units, Lexicon makes the absolute best digital reverb and delay on the market.
Hopefully there is someone out there who has experience with the Omega who can fill in my blanks.
Good luck.
(The reason I initially recommended the Mackie w Firewire option is that I have a problem with the latency built in to almost every computer based recording solution when adding tracks to something already partially recorded. I still like that option, although you can't go back and change anything--it forces you to get it right in a single take--but I have never beaten the live sound I get off my Mackie Onyx board in my studio.)