TwistedWave is an audio editor that supports many formats.
Among other things, it provides:

• Background processing to allow you to continue working while a long computation is going on.
• Unlimited and instant Undo/Redo.
• Import/export to many formats.
• A clip list that allows you to select chunks of audio you are interested in, and copy them to the clip list, making it very easy to reorder and paste them in a new document.

A fully functional 30 day demo is available.

You can try it, at this address:
http://twistedwave.com/