Miss Snark's First Victim is one my favorite writer's blog to follow. They have monthly contests called "Am I hooked?" where secret agents (real literary agents) will critique a 250 word submission from your manuscript. And they also have great community for writers to talk to their peers.
This month they are holding a "Talkin' Heads" critique, where you can submit a 250 word sample of dialogue. And this is particularly great because it is open to incomplete manuscripts!!!
Head on over and have critquing some of the submissions! Just remember to do Number 26 which is mine!!! :D