What standard zoom lens?

Now that I've pretty much made up my mind about purchasing a Nikon D90, what standard zoom lens should I buy to go with it?

The 18-55 f/3.5-5.6 VR that came with my D60 is apparently not a bad lens but I'd feel strange buying the same lens again. I say this because I am selling my D60 as a kit to a friend of mine, not just the body.

Sigma has made a 17-70 f/2.8-4.5 and an 18-50 f/2.8, as well as an 18-200, which I'm not really looking at, seeing as I have a Nikkor 55-200.

The Nikkor 18-70 is apparently not better at all in terms of image quality than the 18-55, but the build quality is superior.

Tamron has also made a 17-50 f/2.8.

All in all, there are quite a few lenses to choose from, I just don't know which one to settle for.

SIGMA 28-70/2.8 EX DG ASPH or SIGMA 18-50/F2,8 EX DC looks quite good. Basicly they "EX" series looks quite good.

Tough first are designed for 35mm which means you'll get 56mm view instead of 28mm.. probably not what you want.. second will be more like what you want.

Anything acceptable from Nikon is really expensive.. Tamron results looks less then desirable..

But I'm demanding person. :)

One usefull link .. Sigma Nikkon lens reviews

After making some exploring, I'm kinda glad I've bought something that can use all 4/3 lens (and some more with adapters..).

I've had the sigma 18-50 2.8 EX Macro HSM for a few months now and am fairly satisfied. It's not great at 2.8 but perfectly useable, by 4 it's plenty sharp and that's where it spends 90% of its time for me. The HSM isn't quite as quick as AF-S but it's a ton better than the Tamron built in motor. The Macro feature is pretty nice also, goes down to 1:3.

I do have to say that the thing I miss most is that extra bit of zoom on the long end.

Other things worth mentioning are the filter size (72) and the lens cap. The front element is rounded significantly and the filter threads aren't very long which caused me problems when I tried to replace the stock cap with a center pinch model.

The Sigma 17-70 apparently has some quite severe distortion, the 18-50 does indeed do a much better job. That the Sigma 18-50 doesn't go down to 2.8 isn't really a problem, I have a Nikon 35mm f/1.8G for most of my more pronounced depth of field shots, as well as the ones taken in the dark. I really need the low-end width for landscape photography though.

The question is, is the Sigma 18-50 worth double the price of the Nikon 18-55 Kit Lens? I just keep hearing that it's a good lens and it's making me irritated. :p: