Alongside my set of 300 tab bar icons I have this smaller set, which is totally free to download. The icons are licensed under the Creative Commons Attribution-No-Derivs 3.0 Unported License. Basically if you use them, you cannot change them and must link to app-bits.com either in your app or on your app's website.
70 Pixel perfect icons
Retina and 3G ready PNGs
CC Attribution-No-Derivs License