The Transformers Timeline
Lately I've been watching Tranformers Armada and Transformers Energon on the Cartoon Network. When I was younger I religiously watched the Transformers cartoon after school. Armada and Energon are quite different, though, and I felt kind of lost. So, I looked for a Transformers timeline. That certainly answered a lot of questions.
I also stumbled across unicron.com, a cool site with lots of photos of the Generation 1 toys that I had.