At the time of writing, this chart covers every single story and episode of Doctor Who to date. I've tried to make it as comprehensible as possible whilst not being unreadably complex, and I hope it can help people out as a checklist for what DVDs they're missing, or as a guide to what happened before Eccleston turned up.
Episodes marked in black indicated that those episodes are missing (see the sidebar), for the numbered companions and lettered enemies/UNIT characters check the key on the right-hand side. All DVD and VHS symbols indicate UK/region 2 releases.
This chart is a continual work-in-progress - I'm going to be updating it as new episodes are made, DVDs are released and whenever, god-willing, a missing story turns up from a broom cupboard in Hong Kong.
Note: the non-canon section is by no means comprehensive; it doesn't touch on the novels, stage plays or many of the audio releases, and neither does it mention spin-offs not considered to be "Doctor Who" such as Torchwood or the BBV/Reeltime Pictures videos - I may expand this later, or make a separate chart for them.
Trivia: when I started this, I was just trying to work out whether Jamie was the longest-standing companion. Och, ye dinnae reckon it'd be any other than the wee laddie?
EDIT: Whilst this should have been updated already to include Series 5, computer problems are making this harder to complete than it should. Hoping to be able to get it up-to-date soon, but don't hold your breath. In the meantime, anyone got any cool "silence will fall" theories?