http://www.riverpast.com/en/prod/videocleaner/
Is my favorite. I payed the $30 for it, quite worth it, better at converting than Adobe Premiere Pro or the like.
A very popular free converter is Super(C) which can be found here:
http://www.erightsoft.com/SUPER.html (Horrendous website, direct download
here). I find it fairly confusing and I'm not positive it can do batch converting, but it is probably the most popular converter out there.