The D90 and higher models have an in-body autofocusing motor which allows the D90 to use the older "screwdriver" AF system lenses which date from roughly 1987 to 2009. The D3000 will allow you to mount, and shoot photos with almost ANY Nikkor lens made since 1959. But it will not autofocus with AF or AF-D lenses.
Today, there are many affordable AF-S Nikkor lenses, plus choices from Tamron and Sigma in 3rd party, affordable lenses. All of the newer Nikon lens designs are AF-S G series lenses. Yesterday, Nikon announced a new, very lightweight 85mm f/3.5 AF-S DX macro lens with Vibration Reduction. Currently there is a low-cost $199 35mm 1.8 AF-S Nikkor, plus the 50/1.4, 60mm and 105mm macros, and of course other lenses that are offered "only" in AF-S focusing (200,300,400,500,600, 14-24,24-70,70-200,200-400,etc).
The D3000 will allow you to buy any Nikkor lens and slap it on there and shoot photos. So, that gives you 50 years' worth of manual and AF lenses to choose from. The production total is 50 million Nikkor lenses.