SemLabs just released two free iconsets:
The Free Web Design Icon Set is a collection of 310 icons in PNG format. They are 16×16 pixels and they’re designed to be used on web projects but may also be useful for systems icons and for print. This icon pack is free to use in commercial and non-commercial projects, modify and distribute.
The SEM Labs Icon Set is a pack of 52 icons in PNG format. They are 48×48 pixels and they’re specifically designed for blogs and have an SEO theme. However over the coming months more icons will be added to it to give them a broader scope.
They are released under the Creative Commons (by) Licence.