Here are a number of popular Canon EF and EF-S lenses you might come across.

EF 16-35 2.8L USM and EF 17-35 2.8L USM.
Professional-quality new and old fast wide-angle zoom lenses, used by many photojournalists. Expensive.

EF 17-40 4L USM.
Affordable and optically slower version of the above, popular with advanced amateurs.

EF-S 18-55 3.5-5.6.
Pretty well every 300D/Digital Rebel, 350D/Rebel XT and 400D/Rebel XTi owner out there has one of these, since they’re bundled with most consumer Canon digital SLRs sold. Image quality is OK considering the rock-bottom price.

EF-S 17-85mm 4-5.6 IS USM.

Very popular with users of Canon’s subframe D-SLRs, this lens combines decent image quality with a useful focal length range and has image stabilizing to boot.

EF 28mm 2.8.
Inexpensive lightweight wide-angle lens, suitable for landscapes and so on.

EF 50mm 1.8 and EF 50mm 1.8 II.
Super-cheap lightweight fast lenses, ideal for beginners and advanced amateurs. Take surprisingly sharp pictures for the price.

EF 50mm 1.4 USM.
Versatile standard lenses, useful in low light. These lenses contain micromotor USM mechanisms that unusually support full-time manual focussing.

EF 24-70 2.8L USM and EF 28-70 2.8L USM.
Large, heavy black L series lenses, noted for their high quality. Expensive and popular with wedding photographers.

EF 24-105 4L IS USM.
Very popular and quite expensive L-series image-stabilized walkaround lens.

EF 28-70 3.5-4.5 II.
Cheap older lenses with a reputation for decent optical quality despite the really low price. Rotating recessed end makes filter use awkward, however.

EF 28-80 3.5-5.6 II-V, 28-90 4-5.6.
Extremely cheap Canon lenses, supplied with many low-end camera bodies as kit lenses. Lousy optics.

EF 24-85 3.5-4.5 USM, 28-105 3.5-4.5 USM and EF 28-105 3.5-4.5 USM II.
Medium-sized, medium-priced and medium-speed lenses popular with many amateur photographers. The 24-85 is particularly popular with APS and subframe digital EOS users owing to its wider short end. Do not confuse the 28-105 3.5-4.5 lenses with their cheaper and slower 4-5.6 cousins.

EF 28-135 3.5-5.6 IS USM.
Popular and versatile midrange lenses equipped with image stabilization for low-light shooting.

EF 85mm 1.8 USM.
Sharp and relatively inexpensive prime lenses, ideally suited for portraiture.

EF 100mm 2.8 Macro and EF 100mm 2.8 Macro USM.
True macro lenses capable of 1:1 closeup photography, yet equally useful as portrait lenses.

EF 70-200 2.8L USM and EF 70-200 2.8L IS USM.
Heavy white L series lenses, favoured by a lot of photojournalists. Expensive.

EF 70-200 4L USM.
Optically slower and less heavy siblings to the 2.8L. Considered a bargain for the price by many photographers, and popular with advanced amateurs.

EF 70-200 4L IS USM.
The image stabilized version of the 4L. Much more expensive, however.

EF 70-300mm 4-5.6 IS USM.
A popular lens for its compromise between size, convenience and image quality. Much sharper than its 75-300 predecessors, and image stabilization is a big plus. Not to be confused with the DO (diffractive optics) lens, which is extremely expensive.

EF 75-300 4-5.6.
Commonly available cheapie-series telephoto lenses (see below). Ubiquitous owing to the low price, but optically poor.

EF 1200mm 5.6L USM.
Okay, so these gigantic and insanely expensive telephoto lenses aren’t popular as such, but always feature prominently in Canon’s lens advertising. Canon will gladly custom-build one for you, given a prepaid order. I think they run for roughly the cost of a luxury automobile.
Frankly if you need this sort of focal length you’re better off with the 600mm 4L IS USM and a 2x teleconverter, though admittedly you’ll need an EOS 1V, 1D, 1Ds or 3 to autofocus with it.