It can be useful to look for places that are closest to where you live, as many on lines stores offer much lower shipping for closer destinations. Shipping can be anywhere from $15 to $50. For example, if you live in Illinois, and are ordering coral from coralcompulsion.com, shipping is only $15.
Some sites I've used and heard good things about:
- Happycoral.com, stock is constantly changing but they often have a good selection of zoas for 5-7$ a frag.
- Reefs2go.com has a lot of good selection and has some nice free shipping packs
- Liveaquaria.com usually has very healthy livestock and ships fast, also they often provide valuable info on corals on their site pages.
I'm sure others will chime in with personal experience and other good vendors.