Well, while a good soundcard will have lower latency, just getting different drivers for your existing soundcard can help a lot. There are many 3rd party drivers that work much better than the original drivers when it comes to latency.

I tried this a while back when I was using Windows and it helped a lot. But of course it's easy to mess things up too :)

On Mac, the standard Core Audio drivers have basically no latency at all with the built-in soundcards. Depending of course also on how many tracks you're playing simultaneously in your sequencer.