I got a 400D this summer after deciding I really wanted a SLR, enough to spend my whole summer working for one, and I love it.
I found that the kit lens wasn't cutting it for range and speed, and got a Sigma 70-300 and 50 f/1.8. Now I want a general zoom that is faster, hopefully has IS, and has better AF.
The most important factors for me are faster autofocus and better low-light capabilities. I know I can't approach the low-light capabilities of the 50 1.8, but something better than the kit lens would be nice. I was thinking there are two ways to approach this: IS or a faster aperture. I would like IS, but it isn't necessary.
Whether it's an EF or EF-S doesn't matter; I won't be upgrading to a full-frame body for a long time. Brand also doesn't matter, as long as it's a good lens.
I realize that an L would be ideal, but I don't have the money (and spending <$1000 on a lens isn't feasible in the foreseeable future)
I've considered are Canon 17-85 IS USM, which looks quite good: USM and IS, and can be purchased used for quite a discount.
Any opinions or lens recommendations?

