You left out the most dominant backorder company of all, Pool.com
Another one is NameWinner.com, and eNom also has their own service called Club Drop.
If you backorder a name at SnapNames, Pool.com, NameWinner, GoDaddy, and eNom you're darn near guaranteed to be able to aquire the name when it dropped. Most of these services use an auction format to sell the name to the highest bidder.