mixing/editing -- wavelab
creation -- cubase, protools, and logic (mac only)
none of these are by any means cheap and offer a lot more features than is needed by an amateur.
for mixing/editing.. if you want a multi-track editor, a cheaper alternative is audition.. if you don't, there's sound forge.
for creation.. cakewalk sonar home studio can be had for about half the price of cubase.