Yes, we all know iTunes sucks, but some of us are stuck with it. Anyway, I was receiving an error like "iTunes Library file cannot be saved not enough memory". I didn't save the exact error, I should have.
Anyway, I loaded up process monitor and noticed a lot of access errors to ATH.exe. This I immediately realized was because many months ago I renamed ATH.exe to something else because it was constantly sucking up 100% CPU. I didn't put much thought into it at the time because it solved my immediate problem. Once I renamed ATH.exe back, the memory leak in iTunes went away.
So in summary, to fix a memory leak in iTunes, check process monitor (sysinternals) or uninstall all Apple software (iTunes, Apple Mobile Device Support, etc.) and reinstall it.