I have the Canon Rebel T3i and LOVE it. It's an introductory model but has a lot of good features and has the ability to take great pictures!
I have a Canon 30D, which I adore. I bought it used to save some money, but it still works flawlessly.
I also have a Canon 30D, which has the magnesium alloy body instead of plastic = great for those of us who drop things a lot at the barn. The best DSLR advice I've ever heard is to buy the cheapest body you can get away with, but the most expensive lens. I bought my body used off of Amazon with a $400 lens (plus two batteries and a case) for $700, a few model years old. Bodies (shutters, especially) wear out, but you'll have the lens forever (they are backwards compatible). Also, Canon and Nikon are considered to be pretty much equivalent in quality. I chose Canon because my friend had a Canon and I was comfortable with the menu and handling, but you can't go wrong with either one.
Start with the Canon Rebel XT(whatever it is now). That is a great camera and super affordable. I had two before upgrading to the Canon 60D, which I also love.
I have a Canon 7D which I adore!!!!!!!! Although I haven't picked it up much here lately, I've been way to busy.
I have a lot of opinions on this (being a professional photographer and all) but it all depends what your needs are. I adore my D700 (nikon), but any camera is only as good as the lenses it has (that's where you should really spend your money). That said, if you're looking for something that's not too bulky, I can't say enough good things about the new mini DLSRs. I have a Sony NEX, that has interchangeable lenses and takes HD video. it's small enough to stuff in my pocket but also has nice compact zoom lenses available. I know Olympus makes one called the PEN and Lumix has one too. I bring mine everywhere because it's so small and the quality is amazing.
I have an older Canon Rebel (maybe 6 yrs old) and I love it. I think my friend has a Niko and it is really nice too. My mom has a larger Canon and it is a lovely camera. Not sure that helped at all but happy shopping! :)