New lens: 3rd party and canon

[sprocket]

Hi Guys, been a while between posts for me here but good to be back

In the market for a new lens thats going to be good in low light conditions, so thinking something at about f2.8

I'll be shooting a lot of indoor scenes, nightclubs and partys - that sort of thing. Will be shooting with a 450D and my 430EXII speedlite.

I'd love to pick up a canon 16-35 f2.8, but at about $1700 online its more than I really want to spend.

So I've been looking at some other brands, in particular the ones below.

Tokina 16-50 f2.8
Sigma 17-50 f2.8
Tokina 16-28 f2.8

As well as the Canon 17-55 f2.8 - and am interested as to how the above compare?

I've read some online reviews and the Tokina 16-28 seems the best (and most expensive) of the three, but wonder if anyone here has any experience with these lenses?

Opinions required!