Audacity is a little gem under the free sound editors. It has a great noise removal feature which can supress static background noise as if it was never there. (Use it sparingly though, it can create weird effects. See How to reduce static in my audio? for more info about avoiding static.)
There are many other useful features that you would expect in expensive software packages. However, the application has a couple of quirks you have to get used too, that is why the rating is 4/5. Audacity will be covered in the Software reviews later on. Stay tuned!
The software is relased under the GNU license, open source software agreement.
Download Audacity here >>.
Audacity is great, I often use it!