Yahoo UI Design Stencils (for Visio, Omnigraffle)
developer.yahoo.com
developer.yahoo.com
If Yahoo! were to be gobbled-up, Flickr and the Yahoo! Developer Network would be the only things I'd pray aren't canceled.
I don't know how strong the business case for this is for Yahoo's bottom line, but it does seem like it's cheaper to define the standards rather than play catch-up on converting two or three years down the road when everyone settles on a set of conventions. It's also good to be a thought leader among developers and designers...frankly, I feel more warm-fuzzies for Yahoo these days than Google, primarily because Yahoo has done so much for improving web design and making UI development on the web really nice and predictable. They've begun to turn it from a black art into an engineering discipline (vision and taste still matter, but a lot of the usability problems have been formalized into a coherent system rather than a pile of guesses).
It's also extremely uncreative and lazy.