Audacity is quite good, free and open source.
It comes preloaded with a wide range of filters and effects and is compatible with, amongst others, VST plugins (i.e. as used by Cubase), if the built-in ones doesn't satisfy your needs.
I've used it for recording radio broadcasted concerts, transferring cassette tapes to CD/MP3 and editing recordings when I was out playing with my band (mainly EQ, compression and cutting).
Here's the official feature list.