I like Drumperfect.com for purchasing shields:
http://www.drumperfect.com/drum_shield_super_store.asp
I like this place because it has several features other than just selling the drum sheild. For one thing, the free advice feature they offer isn't a joke or a gimmick. I've recieved wonderful service from this place. But of course, the shield selection itself is great, too. Mostly I like them because there's a lot of variety and lots of things in different price ranges. I got a pretty nice shield for a comparatively cheap price, which is good, as I'm a student musician and cannot afford the best equipment yet.