Zamzar is a good free file converter that supports many file formats. It is very easy to use and lets you convert files online without having to download any software. It is not the first service or software I would try, but it works for what it does.
I found it to be slower than most other online file converters, but if you've been disappointed with other file converters, need to do your file conversion online, or have an obscure file that other converters can't handle, give Zamzar a try.
Here are some features I think are worth mentioning:
I like that Zamzar is so easy to use. It’s easy to recommend because they don’t force you to create a user account, and the 50MB file upload limit is pretty decent for most files. While I don’t like the slow conversion speeds I sometimes experience, I do like using Zamzar because of the huge list of supported file formats; I can usually count on this site to support an output format I want my file in.