Probably the best suggestion would be to go into a camera shop and ask for
some Canon lens literature. In that kind of stuff they will have pictures
of each lens, the type of photographs that they are useful for, and
specifications for all of the lenses. Of course this is Canon (or Nikon or
whatever) propaganda, so take how wonderful they are with a grain of salt,
but they will be informative.
Then hit the library and try to read a bunch of photography magazines paying
attention to the type and focal lengths of the lenses pro's and semi pro's
use. The camera, lens chosen, film (if any) and exposure information are
usually part of the caption in these kinds of magazines and it's useful to
see what choices that the pro made. You probably won't want to spend $1500 +
for a 70-200 f2.8 lens to start off, but a slower version will take the same
picture at f8!
As for your first lens I'd suggest the Canon 24-85 f3.5/4.5 (as I chose for
mine). It's relatively inexpensive, sharp, smallish, and would provide
coverage (with the 10D) from moderate wide angle to moderate telephoto.