http://www.lingq.com has the option to either pay (it's pretty cheap), or swap (You give lessons in your native language to earn points, and spend those points on lessons). I haven't used it yet (I'm still too much of a beginner) but I hear people are quite good there. After your 15min conversation they'll send you a report of suggestions/corrections you can make.

Some free options, none of which I've used, are: http://chatonic.com/ http://www.italki.com/ http://www.babelyou.com/ http://www.mylanguageexchange.com/, http://www.sharedtalk.com/ http://www.lenguajero.com/ (Spanish) http://vraiment.info/parlezfrancais/index.html (French)