Eligius is growing and might be worth checking out if you want a big pool:  http://eligius.st/~gateway/

I started there to learn the ropes.

I have since moved to smaller pools (https://give-me-coins.com/ and http://hhtt.1209k.com/).  End of the day, the payout is the same (in theory) and I bought into the "smaller pools are better for the network" argument.