Best Editor for less than $100 out there... but that's really not saying much given that everything under $100 is pretty much junk.
I like being able to count on Audacity -- if I'm not near my own personal machine and I've got some editing to do, I can always download Audacity and know it'll work. But it's got some serious issues, like the fact that it can't and does not and will not edit a file directly but resamples and converts every file into the "Audacity" format. Open, edit & save the "same file" 10 times and it nasty artifacts begin to arise. By 15 edits & saves the new soundfile is utterly unusable (unless I'm TRYING to generate the artifacts).
If you really want to do some good editing (i.e. you're not just trimming mp3s for your tunes collection), then you'd be far better off saving up some money and buying something more robust and less harmful to your media, like Wave Editor by AudioFile Engineering.

alej744 OTM

the audacity betas with support for hosting apple audio units, are amazing!

Not only is it the best audio manipulation/editor I have found, but it is also free!

Excellent. Practically the only app. I used on Windows that I still use on the Mac - it's free & robust. I've transferred a few dozen cassettes and vinyl LPs to mp3 & had great results with Audacity's noise reduction and equalization features. There's a good starter tutorial here: http://curriculum.union.edu/tips/audacity.php

I like this application, I agree, it does take some time to be able to use it properly, but it can produce some very good results. there is a beta version at:
http://audacity.sourceforge.net/download/beta_mac

it's the best app to record audio and make podcasts!

Extremely ugly / extremely useful.

Its GUI toolkit, WxWidgets, makes it look like an ugly thing, and the releases only come about once per year, but even so, it's an amazingly good piece of software for what it is: a general sound editor, with some advanced features.

Last time I looked at Amadeus it was pretty useless. Have they developed it to a point where one can actually do stuff with it?