I've had some success on elance. The trick is to be extremely selective about who you will talk to. Also, refuse to compete on price. The good clients will see the difference; if they're comparing you against a large firm, you will be competitive on price even if you're making a reasonable hourly rate.

Lately I'm starting to think that both of these points apply to freelancing/contracting whether it's online or through some other channel.

Also, build a decent portfolio of your work.