I honestly don't think you'll go wrong with any of the cameras you're looking at. Canon & Nikon are like the Coke & Pepsi of the DSLR world, so it's really a matter of personal preference.
However, the choice you make right now will be the one you'll be with for the rest of your DSLR career. ie. once you choose Canon, you'll be staying with Canon and its products for a long, long time. It'll be expensive to switch to Nikon (or vice versa) later on down the road. No pressure!
Be sure to stop by your local camera store (not just
Best Buy...I'm not sure if they carry all the above DSLRs) and hand-hold the cameras yourself to make sure they "feel right" to you.
I've got a Canon DSLR, so I can tell you more about Canon stuff. The T1i is a great camera that now includes HD video. Canon is well-known for its dozens and dozens and dozens of high quality lenses, so you'll have
plenty of lenses to choose from. If you ever decide to rent a lens, there are tons of companies renting Canon lenses. If you ever want to buy or sell a lens, you can pretty easily find another Canon person to buy from / sell to. If you ever decide to upgrade your camera body, Canon's got a great family of camera bodies to move up to (ie. Canon 50D, 7D, 5D Mark II, etc...)
I'll let someone else comment about Nikon's advantages. Nikon is certainly no slouch in the lens department. And I've heard really good things about the Nikon D5000. And, as you've already found out, Nikon also has lots of great cameras to choose from.
Not sure if I made your decision any easier. Let us know what you picked (Canon!). Good luck!
