My daughter is an ultimate Doctor Who fan and is insisting we visit the Dr. Who Experience when we visit London next June (as a side trip to Cardiff, Wales). She's also converted me from a casual watcher to the guy on the aircraft with the Doctor Who ringtone. You can imagine how excited she was when we came across this infographic timeline:
I did a bit more research on Doctor Who Timelines and found one by NathantheNerd. This timeline identifies the actors who played the Doctor and his companions for the episodes in seasons 1-6.