Google - you get better at putting in the right search terms to
sift out what you want. Google Scholar is useful too - sifts out
the gazillion sites which just repeat the same tired stuff you knew
anyway.
I agree that you have to go very, very carefully with Wikipedia,
although the links at the bottom of the page are a goldmine, and
it's perfectly good for straightforward facts that no one would
dispute: if it had got the date of the dissolution of the Batavian
Republic wrong, someone would have corrected it.
I use Google Image/Maps/Streetview a lot. How else are you going to
work out if she can... when they are... no, that was in the erotic
short story I'm not allowed to own up to, so I can't tell you or
I'd have to kill you. But Google Image found the Smithsonian site
for me, and answered my question.
I'm lucky in teaching for the Open University, as they have the
most fantastic electronic library, which gives access not only to
things like the full new DNB and OED, but also JSTOR and the other
scholarly archives. I'm in mourning for the goldmine that was Deb's
Historical Research Page, as that seems to have vanished. (Moral,
if you like and use a site, don't keep putting off clicking the
'donate now' button...)
But books still win. I'm shameless about actually buying them,
because you never know when they'll save your life at 10.30 one
night two novels from now. And browsing them always brings up
things you wouldn't have known to Google for.
I've ordered British Library books through my local public library,
though inter-library loan of all sorts does take forever. It's a
huge help to be able to search catalogues online, though. The
British Library I find next-to-useless, what with not being able to
borrow the books (no use to a single parent with school-aged
children), and having to order them (how can you be sure they're
what you want?) and not being able to browse the shelves when as so
often you don't know what you want... So I belong to the London
Library, which was founded in something like 1865, precisely by and
for people who are driven nuts by the BL.
http://www.londonlibrary.co.uk/index.htm. Their
electronic library also gives you access to lots of things, and you
can even run a postal account, if you don't live in London and get
books posted to and fro. And these days they have a coffee
machine...