Best Variety: http://www.vampsandtramps.com/
Vamps and Tramps offers a startling selection of 20+ bullet belts, including bullet bracelets and belts of various colors:
Best Price: http://www.dracsplace.com/
Although many of the cheapter, non-authentic bullet belts can be found in costume stores, I bought this same
belt years ago and it does not look as cheesy as some other Halloween look-alikes. At this costume site it is only $16 - a steal compared to the 70-100 price tags at Vamps and Tramps!
For a more understated belt, check out the bullet buckles at A Well Dressed Bullet on Etsy, which run for about $20 and come in a variety of calibers:
More awesome ammunition can be found at A Well Dressed Bullet, including bullet necklaces, keychains, and my personal favorite, the bullet pen! And, of course, I have to include the bullet ice tray, available at Amazon and Urban Outfitters: