the entry level nikons are great as are the Canons. I say, get something that fits your hands, seems intuitive to you, etc. That being said...I'm a fan of B&H photo (www.bhphoto.com
) they have a used section and have the best prices on new stuff. I think the Nikon D5000 is a GREAT camera as is the older D3000 and one of my favorites...the D40/D40x (I have the D40x). I'd search for the D40 for an inexpensive used entry level nikon.
Another important thing to look at are lenses and collective knowledge. Lenses: I think Canon has several different mounts, be sure to get a configuration that will allow you to grow into the hobby. Nikon stuff has the same mounts (to get specific, some will support Auto focus other's won't). As you get more into it, let me know what questions you have about lenses.
Collective knowledge: so...I chose Yaesu 'cuz alot of you have that brand and there's alot of knowledge. at the level of money you are spending on a camera or ham you're getting a great product. I'm a Nikon guy and bet there are an equal number of Canon guys in the club. they are both top of class.