This is an older thread so I've got to dig through my brain (haha-it's early), but I believe the lense I used is a Tamron 17-50mm f/2.8. Tamron makes some great lenses that are decently priced. I think that one was $500 or $600, which is a great price for that sort of lense. I actually have another one of their lenses, too-a 28-75mm f/2.8. I shoot with Nikon digital SLR's-a D200 and a D70 right now, but Tamron makes lenses that are compatible with Canon SLR's as well.
You can probably tell, by looking at the first two photos (funky white balance-they're pretty yellow), that I don't always take my time with snap shots of my pets.