There's one really important date that I'm having a hard time pinning down.
It's relatively easy to find dates for a historical timeline stretching back to the beginning of time. It's a much harder problem to build one looking forward without having a date for the end of the world. That's not to say there is a shortage of predictions. The thing is, if a predicted date proves to be accurate then the completeness of the project is likely to be the least of my worries. In fact the date has been predicted so often that it could make for an interesting timeline in itself.
If this sort of thing tickles you, you may like to strap on your tinfoil hat, smoke 'em if you got 'em, and head over to 220 Dates for the end of the world.