I use Goldwave. I think it's at www.goldwave.com but it's free to download and try. It's really good because it has a lot of stuff like noise reduction and voice alterations. One thing, it can only save in .wav format but if you download the plugins like razorblade that it has links to on the website you can create and save mp3s as well.

I used it to make radioplays a long time ago.