Well I'm about to start looking at buying my first zoom lens but I'm not sure where I should start.

So far I've been using the 50mm f/1.8 on my D90. I don't think I'll need heaps of zoom (the lens on the Canon film SLR I borrowed was 18-85 which was a fine amount of zoom for me, though a little bit more wouldn't hurt). As for the budget, I'd prefer if it were under $400. But if you can convince me I can save a bit longer.

Also, are third party lenses as good as Nikon lenses?