I use the Yamaha S-YXG50 softsynth on a laptop when I need accompaniment for acoustic piano gigs. Click here for more info . It sounds way better than any of the Roland variety, and most of my midi files are setup for XG anyway.

BTW: the Tascam US-122 is a great audio I/O device for recording and playing back audio (I have one) but it isn't a sound card per se (no soundfonts - it wouldn't play MIDI files alone)... you'd still need a softsynth with the US-122.