I've tried a lot. The cheap Sun detergent works ok if you're on a tight budget. For us, the best has without a doubt been Tide powder. If you don't like the strong Tide smell, you can get the Tide "Free & Gentle). I had absolutely NO LUCK with special CD-only detergents. Most of them don't actually contain any soap. Mystery solved right there as to why they weren't getting my diapers clean.
I really wanted to love Rockin Green because of the packaging and the yum smells, but it just didn't work for us. :(