Over the years I've used Craigslist, Now Casting and Breakdown Services, Ltd. to cast TV Shows, Promos , Online video and even French Maid TV.
As I've started casting the next episode of French Maid TV we have been using Breakdown Express from Breakdown Services, Ltd. which is a companion site to Actors Access. Breakdown Express let's you post a casting notice for a particular roll. Then actors, talent agents and managers can then submit talent to audition for that part.
Once an actor is submitted you can then look at their head shots, photos and resumes and send them a message if you are interested in calling them in for an audition.
There are a few little pet peeves I have about the interface of the site and it's only available to large cities but I do like it better than the other options. Over all Breakdown Express is an extremely valuable tool and best of all it's FREE.