I have a small website, which links to e-bay for sales:
www.musicians-samples.com
They're cheap. You can listen to examples to see if you like the snare sound.
Also, I would recommend checking out any of the session series drums from Sonic Implants. IMHO, these are the best "sounding" acoustic drum sample I've come accross. The only problem is that, at most, there is only 4 velocity layers per kit piece. I use the kick sample in a lot of the rock/pop recordings I do.
NS Kit is very cool, and free as others have mentioned.