I own the SB400 - I think it's a wonderful little flash for what it does. If you're getting for a good price used then it's even better. Getting the SB700 would be even better but I think there is value in owning both of these flashes.
I agree with James. Although I did the same when I first started with my D80, I bought a SB 400 too but it didn't last that long. So I ended up with the SB 600 at the time. It's either save up some more and go bigger or stick with the budget plan and just upgrade/pay more later. You can also try some of the 3rd party flash like Nissin, Metz, or yongnuo but they probably don't meter with your camera just the basic flash. The built might be a little questionable but you get what you pay for. Good luck and welcome to the forum.
The SB400 is nice, just realize that it's basically an on-camera flash on steroids. Good for general indoor photography (especially bounced). Outdoor use is pretty limited unless you're close range. I wouldn't try to shoot formal portraits or anything with it though. I'd grab a flash diffuser for it to avoid the flat flash look like this one: Amazon.com: Opteka Flash Diffuser for the Nikon SB-400 External Flash: Camera & Photo