[2]: http://trollim.com
[3]: http://www.codeyouridea.com/coders/
[4]: http://www.happyjobsearch.com/
I'd have to be at my home desktop and check my history for a good list of links, but I got to use a handful of competitors when I was looking for work a couple months ago. I'd have to try this one out to be sure, but the extra polish plus the ability to use the interviewee's own IDE could be huge advantages.
Their approach is different/beyond watching the candidate code.
(I am not affiliated with them in any way.)
I always wanted to make my own challenges that would have to be automatically solved by potential candidates, and here it is! Glad someone else did this already.
Edit: I see codio.com does this as well