There was a great plugin for iTunes in this months MacWorld magazine, Volume Logic from Octiv.
I COULD tell you how cool it is but, why? See for yourself. There’s a 14 day demo that works equally well with both Windows and OSX. Should you decide you wanna keep it, it’s only $20.
The Volume Logic plugin boosts the gain and limits levels for optimized output much as a board op does at a radio station, constantly adjusting levels to get maximum output. It’s no wonder though, they make the software radio stations use.
You’ve gotta check this out. If you think you don’t need this then you’ve never heard it. Phenomenal.
They also have plugins available for WinAmp.