I've been using
www.goldwave.com for a very long time. They have a time limit for the free version, but all it does is start asking if you want to buy it, which is easy to ignore. Every now and then I dump it and re-install just to make that go away, but I've never had any real problem with it.
I made the mistake of ripping all my CDs to my hard drive in .wav format. When I realize what I had done, Goldwave made it very simple to change them all to MP3. Batch converter works perfectly.