Monkey's Audio is my pick. Nero supports it with a plugin http://neroplugins.cd-rw.org/ . If you prefer open-source, than FLAC, but Monkey's is a piece of finest quality programming.
guess I'll get Monkeys audio. Can I burn monkeys audio and mix it? I want to create my own mixes. So far I've seen mp3 mixers.
I use Monkey's, FLAC and Wavpack (I like its "high bitrate lossy file + correction file = lossless" feature). As it's probably the case with mp3 mixers, all processing is done after converting to .wav. Afterwards the result will be compressed again. With lossless formts there'll be no transcoding quality loss of course. If you use CoolEdit (=Adobe Audition) you can get input plugins for some lossy formats at http://rarewares.hydrogenaudio.org or at http://www.ca5e.tk .