Another option, with the community atmosphere is italki.com.
I just had a look at it and, again, I would say it's okay as an addition to "real" learning, e.g. a language course with a teacher, CD-ROM, or maybe some self-study book.
Another thing is that I can't put myself to trust the quality of such online private tutoring as offered via Livemocha or this italki.com; I guess I just wouldn't know how to find out whether they are competent or not when there is no language school/some other kind of institution to support their credibility. Guess I'm a bit old-fashioned, maybe ;)