I have used the Delta-44 and Delta-66 PCI interfaces from M-Audio with great success and I have a PreSonus Fireware interface too. If the interface has ASIO drivers, that is the best ticket in town.

I typically record vocals with already recorded instrument tracks ... the setup that I have been using has been to play the "combined" audio (of whatever tracks are already recorded) is by taking one of my smaller channel audio mixing boards and have my PreSonus play out to my mixer and route my vocal into the mixer while taking the the raw audio via my Insert jack back to the Presonus and the combined sound from the Main Out on the mixer to speakers. This way, the singer can hear themselfs real time with no effects etc. along with the previous tracks (music and/or vocals).

It might sound like an over kill solution but it is the crazy version that works best for me while ensuring that I have almost no sync problem between the tracks later.