Source for low cost redbook CDs

I'm looking for any recommendations for good sources of CDs with a large inventory of music and reasonable or low purchase/shipping costs. Currently a member of which offers a shipped CD for only $6, which seems to be the best I've found to date. Only problem is that they've got a somewhat limited inventory. I enjoy a wide variety of music - classical, alternative, christian, old and new rock etc. Any suggestions?
ebay, local used Cd stores, (patience, etc). more often than not ifI'm buying new, I buy from amazon with supersaver shipping and use the link from AudioAsylum, so Rod get a small kick-back. (Sorry Ernie!)
In California = amoeba and streetlight are great. Also, Rasputin for brick and mortar stores.
Many thanks for the excellent recommendations. Even though I use Amazon a lot for woodworking tools and books, I never thought to try them for music as well. Duh. One of my resources to check out new music is our public library system which has a wide range of styles. Thanks to your input, I will now be acquiring more music than is responsible.
I've had the best luck buying used CDs from marketplace sellers (there are hundreds of them, perhaps thousands, so it's a huge marketplace, and stands behind and guarantees your purchase). I've bought a great many CDs this way over the past three years and found it very efficient (saves a lot of time and running around) as well as highly cost-effective.