1,401 icons in 26 icon sets
Free Large Twitter Icons picture a famous Twitter bird in a variety of styles and situations. The set also includes icons for a Twitter sign. Each icon includes 6 sizes: 16x16, 24x24, 32x32, 48x48, 256x256 and 512x512 pixels. A 32-bit color scheme is used, making the set compatible with Mac OS and Windows. In addition, there are 3 states (normal, hot and disabled) provided for each icon.
More quality vector and raster icons are here: http://www.aha-soft.com/iconsets.htm