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The D5000's decent, it wasn't a HUGE seller but it's still a solid machine. I'd either go for the Nikkor 18-200mm or the Nikkor 16-85mm. Both two wonderful lenses! I'm actually saving up for the 16-85 myself, to mount on a D7000 which I hope to purchase soon.
The 18-200 is very good for all purpose, go wide at 18 or tele at 200, it may be the only lens that you need! The newer model features Nikon's VR ii technology, which compensates for hand vibrations. It's better than the VR i, although that's not to say that VR i is bad. This isn't the sharpest Nikkor DX zoom, although for the price, you're getting a fine tele zoom for all use.
The 16-85 gets a bit wider than the 18-200, and it makes a fair difference. If you compared a 100mm lens to a 102mm lens, there wouldn't be a big difference. Although if you compared a 15mm lens to a 17mm lens, there's be a bigger difference. Small numbers make bigger differences when going W/A. But that's not to say that you won't notice the 115mm difference between the two on the tele side, the 18-200 certainly is better for getting up close. The 16-85 is relatively fast (F3.5-5.6), it's one of the sharpest DX zooms around, plus the VR ii is a great bonus.
So, you couldn't go wrong with either of these lenses. They're both exceptional, and would greatly improve the IQ, plus give you some more versatility. If you really do want to upgrade your body, the D7000 is the way to go. Plus, either of the lenses that I mentioned previously would go great with the 7000.
I hope that I helped!