Brakleen is a disc brake cleaner that you might find in the automotive section of most department stores. (And obviously at stores like Napa and AutoZone.) It is sold for cars and motorcycles, but has many uses.
Pros: It's specifically made for disc brake cleaning, and it does just that. It cleans the pads and rotors very well, without leaving a sticky residue.
You don't have to wipe it dry, either, so there isn't going to be any paper towel residue.
Cons: It's stronger (and more toxic) than most bicycle degreasers. Be careful.
The Final Word
If you have disc brakes, either clean them with rubbing alcohol or Brakleen. I prefer Brakleen because of the nice spray bottle.