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.
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… ;)