Someone just posted a sale on at
http://www.ontheqtinc.com . They have quite a few fabrics for just $3 a yard and shipping is reasonable.
Keepsake Quilting has great fabrics, as does Hancocks of Paducah. You can get printed catalogs from both of those companies.
I have purchased big lots of fat quarters on eBay last year. They came to about $1.25 each, even with shipping, and the quality was great. I think fabric prices have gone up since then, though.
Do you have a specific kind of fabric in mind? Different websites specialize in batiks, country fabrics, cats, juvenile prints, etc. You can narrow down the possibilities a lot if you specify your fabric interests.