I was in an acapella group in college for a semester or so. I enjoyed performing in one, but I don't generally like listening to them. I find most college acapella groups think they're so precious, and I really get tired of the "look! I'm making drum sounds...with my MOUTH!" feel that many have.
That being said, I absolutely love good harmony, as well as traditional barbershop quartets, so go figure.
I do, however, have a good band for you to check out. They are not completely acapella - they do a few acapella songs on most of their albums - but they are funny, inventive, and have breathtaking harmonies. It's a shame that they're not around anymore - they broke up in 2000.
Their name is
Moxy Fruvous. They were huge on the college circuit from '93 - 2000. Going by album, here are their complete acapella songs. You can listen to sound clips on Amazon. Do yourself a favor and listen to them all, because some feature instruments but the harmonies are really what shine.
Bargainville - Lazy Boy, King Of Spain (their most popular hit), Spiderman, Gulf War Song
The B Album - I Love My Boss and Jenny Washington are the only all acapella, but all the rest have minimal instruments - usually just a guitar.
You Will Go To The Moon - Title track, Kick in the Ass (great song!)
Live Noise - one of my favorite live albums - King of Spain, I've Gotta Get A Message To You (unbelievable)
Give 'em a try. They're fun as all get-out.