Tamron 10-24 FTW if you want a cheep wide angle
Ive got a Tamron SP AF 10-24mm f/3.5-4.5 Di II LD Asp. (IF) Lens. To be honest I wasnt expecting to get much use out of this, but as with the other people who use very wide angle lenses its become a firm favourite. Closed down to 24mm and it gives a decent group photo lens. Way out at 10mm and it takes photos of things you couldnt get in otherwise.
It certainly fits in well with the Canon EF 28-135mm. Add in a long lens and you have almost everything covered. Only thing missing is a Macro, if you want to take close ups.
You might want to consider the 60D too, when a full review gets put out.