I'm surprised nobody has mentioned findchips.com. I use it all the time to find which distributors have parts, and if a part numer (or partial part number) pops up, the link takes you to the distributor page that generally has the datasheet.
I used to search for parts on Google, but that's where I found all of my spam. I don't recall the sites, but I always seemed to get links that pretended to have the info, but just linked to other sites that linked to other sites... Then I gave up on Google.
Over the weekend, I've been experimenting with DigiKey, Datasheets and Mouser - running parts from my BOMs through. I did find an electrolytic to not be on Datasheets and a few parts to not be on Mouser. I tend to select parts based on what I can buy at DK, so I would expect to find all of the parts there.
Another site that I find quite useful is: http://public.wsu.edu/~brians/errors/errors.html It's about grammar, not technology, but, though I value function over form, form does help with good communications. This site covers all of those little things like "affect vs. effect:" that I ignored while back in school.
Mouser is where I always go first for parts and datasheets. For live pricing and availability when I don't find it in Mouser, I use Octopart, a specialised parts search engine that gives you real time pricing from several vendors on the same component. The hard work of finding obsolete parts info I leave it to Bing.
Thanks for publishing this list Kristin. I've used several of these sites, but there are others I had never heard of. Like you, I also have had good results with Google scholar to weed out everything that is *not* the journal article or academic publication I'm looking for.