I've got a 350d and use a tamron 17-50 f.2.8 for most of my walk around shooting. Incredibly sharp even at 2.8 wide open at the wide end. Incredible lense for the value.
I also have the nifft fifty f1.8, a super sharp fast lense. It doesn't get much use since I have the tamron, but every once and awhile that extra bokeh comes in handy.
Lastly, i have a budget telephoto, a Sigma 70-300, f4-5.6. Would only reccomend this to those on an extreme budget, as above 200mm it's very soft, and I tend to need manual focus alot on it. Still, I've got some nice shots out of it.
I really want to get an ultra-wide angle lense, but can't really justify the price...I'm on the verge of splurging.
Samples:
Tamron
50 f1.8
Sigma 70-300