I'm looking for a good comparison of custom ROMs' features and quality. I would prefer a comparison that is actively maintained.
The Android Release Matrix at AndroidSpin is pretty comprehensive.
There is also the PDAdb.net Rom Respository, although I don't think it's as user friendsly as the AndroidSpin db.
Last (and least relevant to your question) is theunlockr's list of Android Roms (I just thought it was worth mentioning).