I'm a big fan of sannie (
http://www.sanniesshop.com/). Awesome genetics. Open and transparent breeding. Direct breeder access via private messages, forums, and email. He's also on the more affordable end of prices. Attitude and nirvana both get talked about a lot, and I'm sure they are great sources. They are more retailers though. They both carry seeds by a great number of different breeders who typically don't sell seeds to the public. I personally prefer the breeder access you get with sannie, as well as his excellent customer service. One of the things that has always impressed me is when people post about some problem ordering from sannies, and every response going down the list is "don't sweat it, just email sannie, he'll take care of you", then a few days later is the OP saying sannie is the man and totally took care of the issue