Presumably you mean the 18-70, which was one of the kit lenses early in the DX era. I'm not sure what you mean by "rough" - this is a pretty nice lens, actually.
The first lens that comes to mind for inexpensive but good quality is, believe it or not, the 18-55/f3.5-5.6 AFS VR, which you can get for about $120 in barely used condition. Yes, it's a kit lens, but it performs far better than its price point. I still use one on occasion, in fact.
The other two lenses that I think of are the Nikkor 35/f1.8 AFS and the new Sigma 30/f1.4 HSM DC. Both are fast primes; the Nikkor is about $300 and the Sigma is about $400. A much bigger reach would be the Sigma 35/f1.4 HSM FX - at about $900.
_____ Brian... a bicoastal Nikonian and Team Member
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Wed 01-May-13 10:24 AM | edited Wed 01-May-13 01:26 PM by mklass
The new Sigma 17-70 f/2.8-4 DC comes to mind, although it is a tad over your price range at $500. It seems to be getting great reviews.
The Nikon 16-85 f/3.5-5.6 would also be a good choice and you should be able to find a good used copy in your price range. KEH has a EX+ copy for $415 and they come up for sale here and on eBay frequently.
Both of those are DX lenses, which is fine if you eventually upgrade to the D7100.
If you are going to move to FX, then you might want to look at the 18-105, as mentioned, or a used copy of new 24-85 f/3.5-4.5G VR. Since it is packaged as a kit with the D600, a lot seem to be showing up on the used market already. Again KEH has them for as low as $339 in EX+ condition.
Given that you are primarily using zooms now, and you have a fairly big gap between 20mm and 70mm, I would get a zoom rather than a prime right now.
Save up some extra money and get the new sigma 17-70mm F2.8-4 DCF Macro OS HSM. After using this lens for a week I've been blown away by how well it works. Lightning fast focusing, silent unobtrusive yet fully functional optical stabilization, super sharp pictures, and superb macro performance. Virtually every picture I've taken has come out well.