• Boo
• Download Boo
• MSDN Search - Very handy if you want to look up something in the standard library.
• Mono Docs - Nice source of information as an alternative to MSDN, or if you work on Mono or Gtk specific projects.
• Google - Has a lot of information within its reach. Searching prefixed with ".NET Framework" or "C#" usually will turn up what you need.
• NAnt - A free build tool for .NET