I have recently purchased a second hand lens. A wonderful old 35-70mm f/2.8 nikon, this was a top lens when launched over 10 years ago. It's been super seeded twice with the 28-70 and the recent 24-70. Both I would love to own but are still out of my price range for this type of zoom pro lens. However the 35-70 is a great cheeper option that will give in my opinion excellent results.
I got mine from E-bay and that's always a risk. Mind does not have the cleanest of glass and I have some fungus on the inside. It also has a problem focusing at 35 mm at infinity. But then I only paid £120.00 for it and they seem to sell for about £280 most of the time. That being said it's a testament to the quality of this lens that it still performs so well. I really enjoy the shallow depth of field on this lens allowing the user to create some interesting images and makes you a little more creative once you understand how this lens works. So if like me you don't have an £800+ budget to play with and your lusting after the new nikon 24-70 I would recommend grabbing yourself an optical bargain and have some fun while saving for the more expensive but far superior lens for the future you will have some fun and some great images while you wait.