I have never been able to find a decent royalty-free library of icons but you only have what you pay for, haven’t you?
IconExperience is the best library I have found and I can only recommend it. It is comprehensive and affordable. Incors have just released version 2.0 which has more than 2000 icons and now includes the 128*128 format.
If you know any other valuable source of icons, please comment.