You guys forgot all the BEST Baton Passers in the Game!
This guy is the best Baton Passer in the game. It will make sure that you get atleast a Baton Pass of Speed, due its ablility, Speed Boost. Run a set with Protect, Substitute, Swords Dance and a Filler Move like X-Scissor.
This guy is also pretty epic. It is a reliable Calm Mind Passer, so running a set like Calm Mind, Baton Pass, Substitute and Stored Power is great and great again. This set allows you to set up and if viable, sweep with Stored Power.
Gliscor hasn't been an epic Passer, but fan certainly come in handy when you predict a Switch fro the opponent. Run a set like Substitute, Roost, Swords Dance and Baton Pass so that you can heal, get and get the Sub up.
Not much to say, apart from boss. Shell Smash Passing is so useful. Running this following set will come in very handy. Shell Smash, Baton Pass, Substitute and Aqua Ring. This set allows the healing and sub up. Very good.
Ok, this butterfly is great. With Sleep Powder to assist the Stat raising, it is epic. Run a set lime Quiver Dance, Sleep Powder, Bug Buzz and Baton Pass for best results. This guys is nh favourite Baton Pass.
Mew as you said, has 100 Base Stats all around. This pink kitten can Baton Pass over a bog variety of moves. I won't recommend a set for you here, due to there being so many variations in what it can have.
Celebi, being not much different from Mew in Stats is also a good Passer for you. It can pass over Nasty Plot and Calm Mind, two very useful moves in the current Metagame. The set again can vary so I will not give you one.
Ok, this bug isn't very fast and doesn't have good Defencive stats, but is filled up with the delights of its Ability, Prankster. This means it can Pass over Tail Glow very quickly and also get the Baton Pass of first in play.