O’Reilly has produced an interesting poster about the History of Programming Languages. But beware: the PDF file is 39" wide, probably because it covers every minor version of every programming languages, rather than just important milestones. Apparently you can also get a printed version of the poster for free when you order two books from O’Reilly.
There’s also a corresponding Wiki, and of course a lively Slashdot discussion.
Would you have thought that there are over 2500 documented programming languages? That definitely lets the relatively few languages that I know (or have known at some point) look pretty measly… ;)