I use Memorex black CD-Rs and Mitsui. black discs are pretty good, but as someone mentioned tend to have a warmer sound. Which is not at all a bad thing in some cases. I use Mitsui for more critical stuff. But in any event, to me, the copies don't sound as good as the originals, despite the fact that some people say this is the case.
You can get Mitsui discs at americandigital.com
Be aware though, that some cd transports and players don't read CD-Rs. So before you buy a 100-pack, make sure they work in your player.