Richard, the Nikon D40 has been out long enough now that you can find some deals on them. Probably much better than these but this is what's available right now on Craigslist in your area.
Nikon D40 DSLR with 18-55mm AF-S DX Zoom Nikkor Lens
Or search a bit for a D70
nikon d70 body
I don't really know Cannon but I'm sure there are deals to had there too. The thing to keep in mind in choosing between the two is that used Nikon lenses are cheaper and more plentiful and that is where you want to spend your money!
The camera that Benny bought is not a DSLR but does have a really nice Zies lens. The same quality lens for a DSLR would be very pricey even used. But....like I said when those cameras break they are a throw away because they cost more to fix then to buy another used one.
On DSLR's you can check the click count which is also important. I can't remember how many clicks is too many but a simple search would tell you that.
If you find something still under warranty make sure it's an American camera, not a gray market one. I have a friend who also bought a new D90 but unknowingly bought a gray market one and of course it has problems and the warranty is not so great to say the least. I told her to return it as soon as she found out but she decided not to and now regrets that decision. She's now looking for another camera, a full frame Nikon with an American warranty!