While we're playing with logos, I should not that Wikipedia also needs a favicon.ico file.
What this is:
When people bookmark wikipedia using Windows IE or Konqueror (KDE, typically on Linux), their browser requests 'favicon.ico'. This is then used as a fancy little symbol in the bookmarks list.
It's neat!
Actually, this website has some free ones, but we should (as always!) check the license, because we'll probably want to redistribute it.