Applejack, what did you shoot with before? I have found that most people gravitate towards one of three areas, zoom, wide, or portrait. People tend to have a particular focus on one of these three formats. Perhaps you do also.
A lot of people recommend a moderate sized walk-about lens, such as the 24-105mm F4 L, or the really sharp 24-70mm F2.8 L. These are excellent lenses, but don't do any one thing really well, so I never enjoyed them much. Others swear by them and use them everywhere and anywhere.
Personally, I like wide. I love my 10-22mm Canon lens, but what I get the most use out of is my almost as wide 16-35mm MkII L F2.8. I also have a 70-200mm L F2.8, but don't get as much use out of it, though it is without a doubt the sharpest lens I own.
Here is a good site to learn some general info about lenses:
http://www.fredmiranda.com/reviews/