I had some old .mmf files I wanted to convert to .mp3 for ring tones and did some Google searches and got lots of crap until I found FormatFactory .
It's FREE and really, really nice.
Watch for the check boxes in the last install screen that are checked by default to add an Ask.com toolbar to your searcher and an eBay icon to your desktop.
A fun sound file I like to play when we get a blow-hard in the office or want to call bull-chit on them is the Turkey Gobbler. They get mad as Hell. And when they find out this is their dedicated ring tone on the company phones it get more fun.