I shoot a Canon 10D. My wife shoots a Canon 30D and I occasionally steal that one from her. We both shoot, primarily, with Canon's 28-135mm lense.
Rambling stream of thought follows....
I like the 30D a bit more than the digital rebel line. They're all fine cameras, but I think someone that's just starting out could keep from getting overwhelmed by the 30D while the Rebel will start to feel a bit limiting as time goes on.
Nikon has a fantastic line too but I'm not nearly as familiar with their equipment.
For a lense, I love the Canon 28mm-135mm f/3.5-5.6 IS USM. You can buy it from B&H or Amazon for just under $450. I love it so much that I bought my wife one for Christmas (her favorite lense now too). While it's not as nice as the pro glass, it's great for us amateur types. The IS stands for image stabilization. The same concept on Nikon's lenses is VR (vibration reduction). Basically, it allows you to shoot at a slower shutter speed without introducing camera shake (blurring because we all have the jitters).
The big secret to good nature photography is to not touch the camera. You want a shutter release (a basic corded Canon one is ~$70) and a good tripod. You don't need to spend a fortune on tripods and heads, but spend enough the first time (hint, don't buy these from Wal-Mart or Best Buy). Bogen / Manfrotto and Gitzo are both outstanding brands that you can't go wrong with. My wife bought me a setup that I never would have allowed myself to spend the money on and I can't imagine life without a solid tripod now.
One really cheap way to get into macro photography (like my fly picture or the first one, the grass picture) is to buy a close-up filter like the Canon 500D. This screws on the front of any lense (make sure you get the same size filter as lense). At ~$110, it's much cheaper than a dedicated macro lense (which comes with it's own advantages and drawbacks).
For an intro 'what do I buy and how do I take good shots', I'd highly recommend The Digital Photography Book by Scott Kelby. He has a wonderful writing style (think, talking with a good buddy not listing to someone pontificate). The book is a buying list with options (if you are on a budget then get this, if you can afford it get this, if you have so much money you don't care then get this... if you shoot this way, get this) and also wonderful tips and tricks for getting solid pictures. He doesn't go into the whys, just the hows.
For a great intro on composing great pictures, check out anything written by John Hedgecoe. I especially enjoy 'The New Manual of Photography' and 'John Hedgecoe's New Introductory Photography Course'. You're not going to get as much detail as more formal training, but you'll at least get enough information to know why composition matters.
Another great resource is the local community college. The one by us offers an associates degree in photography and, more importantly, has some great introductory courses on 35mm SLR camera operation (by extension, digital cameras) and composition.
My best advice though is to just get out and shoot, a lot. Play with every setting and see how each change affects your final product.
I don't keep up on the latest camera gear, but would be happy to try and answer any questions... including why someone might want a larger sensor like on the 5D or why someone might be happier with a 30D or Digital Rebel.
