My preferences for very powerful .wav editors are:
1. Cool Edit Pro
2. Sound Forge 4.5 (NOT XP)
3. Steinberg WaveLab
I have all 3, and the cool thing about them is that the best tools in Sound Forge and WaveLab are DirectX plug-ins, and you can use those tools in any of those 3 programs in my list. I like Cool Edit Pro's interface the best, but that's likely because that is the first one I learned. All 3 are easy to use for basic stuff but have pretty steep learning curves for more advanced work.
Oh, and they all cost more than $500 (each).
For cheaper tools, Cool Edit 2000 has most of the power of Pro for like $50. Plus it's shareware so you can
try it out.