It's true, the Nikon system allows for expansion from a manual body to an AF one without losing lenses that might have been invested in the manual body.
That being said, I would still recommend a Canon AE-1 with a 50mm f/1.8 lens. This is the camera that I re-taught myself how to take a photo on. Before it I had a full-auto Pentax and it became a crutch, so I set it aside and found an AE-1 w/50mm lens and a flash on eBay for $65.00. The upside of Canon's decision to pretty much abandon all their existing customers and switch to the EOS system is that you can get all the old manual gear for fairly cheep.
Basically if you are willing to focus your own lens and set your own exposure then you can get a top of the line camera for about $100.00. Granted it was top of the line in 1979, but the only advances that 35mm camera bodies have made in the last few decades has been in the ease of use (read: computer compensation for user laziness, ineptitude or lack of patience) area. The only people who really need all the latest technology in a camera body are photojournalists. The difference between life and death for say, a war photographer, could be measured by their cameras ability to photograph automatically and with multiple frame rates. For the majority of photographers (especially new ones) all the latest bells and whistles, while attractive, are not needed and if anything are a hinderance.
Well I am going to step off my soap box now.
Good thread Modafoto!