Other
Colossians: Research Center
Jackpot! This is an excellent resource for researching Colossians. It contains a long list of links to sites about Colossians on the Internet.
Other
Ray Stedman: Adventuring Through the Bible
"Adventuring Through the Bible" is a comprehensive guide to the entire Bible with Bible commentary. This site is an excellent place to start if you are new to the Bible and/or have questions about evangelical Christianity.
Fourmilab Switzerland
John Walker: Colossians
The actual Colossians text, chapters one through four.
Other
New Testament Study Helps
A series of articles (links) on the various books of the New Testament. The author provides background information such as author issues, the general structure of the individual books and more.