Cornell Labs has just opened a new online bird id tool. It's still in beta and only contains about 400 North American birds, but it is pretty cool. I tried three very similar small birds -- Hutton's vireo, Pacific-slope flycatcher, and Ruby-crowned kinglet -- and it got all three in seconds. It is self-learning, so the more queries/images, the better it will get. Try it out:
Merlin PhotoID