Just ran across this vector set courtesy of IconDock

This free set includes 50 icons of the most popular social media networks on the internet. The icons are designed in 32px and 16px vector format. With the vector format, you can scale the icon to any size to fit with your design or use it in high quality print materials. What you will get from the zip package: 32px and 16px in three different file formats: vector EPS, PNG, and GIF.

Icons include:
Delicious, Flickr, Twitter, Retweet Button, Facebook, MySpace, StumbleUpon, Digg, Slash Dot, Mixx, Skype, Technorati, Reddit, FriendFeed, YouTube, LinkedIn, Newsvine, SlideShare, Google, Google Talk, Yahoo, Yahoo Buzz, Netvibes, AOL, Microsoft, MSN, Apple, MobileMe, App Store, Amazon, Last.fm, Mister Wong, Qik, Vimeo, Viddler, Virb, Tumblr, WordPress, Blogger, Posterous, Behance Network, Design Float, Deviant Art, Design Bump, Friendster, Bebo, Squidoo, Share This, RSS, and Email.

Update (Feb 26, 2010):
Google Buzz, Picasa, Bing, Meetup, Ebay, Feedburner, WordPress (blue version), Drupal, Gowalla, ICQ, Metacafe, Yelp, Xing, PayPal, Heart, Star, Podcast, and various color buttons (create your own).

Download:
Either download the attached zip file or get the most recent version at:
http://icondock.com/free/vector-social-media-icons

License Info
This icon set is released under is licensed under Creative Commons Attribution-Share Alike 3.0 Unported License. If you use these icons, please place a link to http://icondock.com. Thank you.
Note: the company logos in the icons are copyright of their respective owners.