Hello Donutboy,
Welcome to TPF!
The magic number you're looking for is the length of the lens, normally expressed in millimetres.
A wide-angle lens will have a focal length less than 28mm (this is a debatable number). So what you're looking for is a lens which is less then that number in length. Most manufacturers should state some stats including this number (usually referred to as "length")
Digital cameras tend to have a magnification factor (when using 35mm film camera lenses) as the sensor is smaller than film. In your case the factor is 1.6x (if the internet is to be relied on - correct me if I'm wrong). Therefore a 20mm lens is actually going to work out at 32mm which isn't "wide" if you're looking at normal Canon lenses - I don't know whether Canon's digital lenses correct for the mag factor.
I can come up with lots of suggestions for a lens, but it really depends on a number of things:
1) How much money do you have for this equipment? (Wider is normally more expensive, as is more light - a smaller f-number)
2) How wide do you want to go? (e.g. 7mm would be very wide, 28mm would be only a bit wider than a standard lens - it would help the good people here for you to say what kind of picture you want to end up with)
3) Do you worry about fish-eye distortion? (do you want the image to look "as is" or to look curvey/strange round the edges, but still very wide?)
4) Do you want to zoom?
Congrats on your purchase, hope you enjoy the forum here.
Rob