How much are you looking to spend? A computer built specifically for recording can be pretty costly...especially when you consider the soundcard you will use. As far as consumer level cards go...an ESI Juli@
or an M-Audio Audiophile 192
is a good starting point. Stay away from anything that is Creative, theyre latencies are much too high (~800ms) for a serious recording setup. A decent studio grade card will have a latency under 100ms. The cards I have mentioned above will run you ~$200.