I took the time to bring my camera in to the store the other day to try out the Tamron 17-50 VC that I talked about earlier. Long story short, it just clicked. (Pun intended.)
First impressions was that it was a lot heftier than the kit; being a constant-aperture lens this was expected, but it was interesting exactly how much larger it appeared on the small 1000D body. The zoom-ring had a bit of friction to it, but nothing I can't see myself getting used to...
I did, however, notice something in my test-shots, which I can't see myself getting used to. While I was pretty satisfied with the image quality, there was a patch in the middle focal length around 30mm that was just atrocious at f/2.8. This went a bit opposite of the reviews I've read which usually put 50mm as the real problem area, which could point to sample variation. (I noticed a bit of the same problem at f/4, but otherwise it behaved as I had hoped.) I will certainly test it more thoroughly when the time comes to actually decide to purchase or not, but there is a strong want-factor about this lens.
There are a couple of options to the Tamron: there's the equivalent Sigma 17-50 which just came out, which is about 1.5x the price of the Tamron, then there's Canon's own ultimate EF-S lens, the 17-55, which in turn is about 1.5x the price of the Sigma. They all cover roughly the same focal length (ie. same zoom level) and they're all constant f/2.8. What separates them is differences in build quality, autofocus and image quality, following roughly the price increments: Sigma has a bit better image quality and autofocus motor than the Tamron, Canon has the edge on both of them.
One thing I would want though is working autofocus in low light. I learned that from the 50mm, there's no point in having a fast lens if it won't focus correctly in low light. But seeing as pretty no third-party lens can have the same level of autofocus compatibility as Canon (as they reverse-engineer the connections), that would mean the Canon 17-55, which I really don't have the budget for.
But who knows, I might win the lottery!