I find SUPER CONVERTER to be really good, it can do about all formats including .dpg, PSP, iPod etc. Google super. Downloading it off the site is a pain though.
go to xilisoft.com they have a video converter that supports any kind of vidoe files even audio files
actually i can never find one converter that can do all the job right. you may need a couple of program to do different type of conversion. for example, rmvb to avi, i found winavi to be the best quality and speed so far. i tried mediacoder, but the quality kind of low and slow. for things like mpeg, tmpgenc is a good one.
I've used tmpgenc Pro a bit and its good (before it got sold off that was, new versions are utter crap), but my preferred video converter is actually MainConcept H264 encoder (which Divx are probably going to wreck now they've bought out MainConcept)