I have been tinkering with Linux to record taglines and interviews for KTEK 88.7fm as well as recording some of my older media, albums and cassettes mostly, to CD. Here are some tools, references, and information I have put together that have helped me.
A good place to start is the Sound & MIDI Software For Linux. It is regurlarly updated and is a good place for new programs and HOWTOs. Digital Domain has lots of good explinations and tips for making audio CD's and recording audio in general.
Audacity is a cross-platform audio editor with some nice effects. I have used version 0.94 but it still has many bugs to it. I have not upgraded yet because there is just too much damned gtk crap to upgrade along with it.
DAP-2.0.2 by Richard Kent has a normalize function that is rather useful. The whole package itself is a pretty good editing utility although it doesn't seem to be able to record the music off the line-in. It also wants to use AIFF. It can import WAV though. (email@example.com) Here is a screen shot.
The more I play with DAP the cooler it gets. It has very good DSP functions, including gate and comp/lim functions, and best of all it has a normalize function. It is written with XForms so it is a bit sluggish on the Menus.
This is a graphical sound sample editor, with recording and playback facilities and a built-in graphical mixer, for Linux. It contains a main record and playback window, a graphical VU meter, and can save to many file formats such as wav, aiff, and au. It makes extensive use of sox, the sound exchange program, maintained by Chris Bagwell (firstname.lastname@example.org). Review
SoundStudio is a good general purpose recording program. I've used it for a lot of recording so far. It allowes for cut and pasting bits of sound files, and has the basic sound settings supported by most soundcards (trebel, base, I/O gain, ...). It also supports effects such as phaser, fade, and reverse. For most recording it seems to do the trick.
Other programs that I may or may not have tried and may or may not be useful