Mark,
a bit depends on whether you have a film SLR. If you have, most of the lenses for film SLR's are compatible with the digital SLR's from the same maker, and you would therefore be more likely to stick with the same manufacturer. I used to have a Canon EOS 500, and when that died recently, I had no hesitation (after a lot of research, mind you), in opting for a Canon EOS 400D.
Depending on the available deals and the lens options you are after, this could well fall within your price range........and I would heartily recommend it. I think it is a wonderful piece of kit, and the controls are quite readily picked up (I think instinctive sums it up quite well).
If you are retaining old lenses to use with a new body, then remember that the focal length will not be the same as it was when used with the film camera. With the Canon the ratio is about 1.6............ie, a 50mm lens on the old film camera will actually be around an 80mm focal length on the digital version. This can be really handy with long range stuff (a 200mm lens becomes 320, which gets you quite close in to that lion 100 yards away!), but does mean that group photos of your family at Christmas might mean you standing 5 or 10 yards further away than you did with the old film camera.
There is a strong Nikon competitor for the Canon EOS400D, but I am not sure of its name. They came joint top of a "What Digital Camera" magazine poll of digital SLR's last year.......and that would also be one of my best tips........go and get a few magazines, google around a bit, and ask as many people as you can.
Good luck.........and I'm sure you will get lots of varied opinions on here......
Cheers
Mike