I'm starting to get asked this question all the time, so I figured I'd throw down a post about it. The first debate is Canon Vs. Nikon, and to tell you the truth at this point in the game it doesn't really matter. They're both great brands and cameras. Nikon has definitely been catching up to Canon and giving them a run for their money. I prefer Canon for a few reasons. The colors I get from the sensor, and the fact that I've been shooting Canon since I started. When I started a few years ago, Canon was the frontrunner in the digital world. They were the only brand that had a full frame sensor, not to mention the image quality was far superior and larger to Nikon, so I got invested. Once you start buying lenses for one brand, they are compatible and interchangeable with any camera within that brand. Recently the game has changed in quality, and Nikon has been releasing camera bodies that compete with Canon. I still prefer the color tones of the Canon DIGIC processors. The reality is that if you have either you are good to go. I don't really even consider any other brand a player in the market. Obviously since I know and shoot canon, thats what I'll be recommending.
Remember, lenses are as important or more important than the camera body. The quality of the image that is projected onto the camera's sensor is what your image will be so if you have great optics you will have great quality images. I love fixed lenses, but for people starting out I usually recommend a few zooms to cover a wide focal range.
That said, you need to ask yourself a couple questions. A: How serious are you about taking photos? Do you want to just have fun, and take better memory photos, or do you want to eventually shoot on a pro level? B: How much money can you spend?
If your answer to A is just wanting to have fun and taking better memory, then you won't need to spend as much to jump into an DSLR.
Here are my recos for this answer depending on your budget. The Canon Rebel is a great series for this scenario for someone who doesn't need or want to invest in a photography career.
A: $1000ish: Canon Rebel series(approx $750) + a 50mm f1.4(approx $350)
B: $1500ish: Canon Rebel series +
C: $2000ish: Canon Rebel series(approx $750) + 24-70mm f2.8L (approx $1300)
If your answer to A is wanting to try out photography with the potential of doing it as a career then you'll want to step it up a little. I would recommend saving up your money to invest more in the beginning then having to rebuy a prosumer body down the road.
The Canon 50D and 5D series cameras are great for this scenario. Purchasing the right one will depend on your budget. Obviously the 5DMKII(my review of the camera) will be the best choice, but is going to be more expensive. The 50D has a cropped sensor so your focal lengths will be multiplied by 1.6. That is the trade off for not spending as much on the body. The crop is something you just have to get used to and work with if you don't want to spend the money to jump to the 5D series.
A: $2000ish: Canon 50D(approx $1400) + 50mm f1.4 (approx $350)
B: $2700ish: Canon 50D(approx $1400) + 24-70mm f2.8L (Approx $1300)
C: $4500ish: Canon 50D(approx $1400) + 24-70mm f2.8L (Approx $1300) + 70-200mm F2.8L IS(approx $1700) these two lenses cover a great range.
C: $6000ish: Canon 50D(approx $1400) + 24-70mm f2.8L (Approx $1300) + 70-200mm F2.8L IS + 16-35mm F2.8L(approx $1500) even fuller range.
D: $3500ish: Canon 5D (approx $2700) + 50mm f1.4(appxo $350)
E: $4000ish: Canon 5D (approx $2700) + 24-70mm f2.8L (Approx $1300)
F: $6000ish: Canon 5D (approx $2700) + 24-70mm f2.8L (Approx $1300) + 70-200mm F2.8L IS(approx $1700) these two lenses cover a great range.
G: $6500ish (my fave lenses): Canon 5D (approx $2700) + 20mm f2.8L(approx $450) + 35mm f1.4L(approx $1400) + 70-200mm f2.8L IS(approx $1700)
H: $7500ish: Canon 5D (approx $2700) + 24-70mm f2.8L (Approx $1300) + 70-200mm F2.8L IS(approx $1700) + 16-35mm F2.8L(approx $1500) even fuller range.
Please note that these are just guestimated figures. It will depend on where you buy your gear for more precise prices. I usually buy everything from BH Photo. I also shoot on the 1Ds MKIII series camera. There's plenty more money to be spent in areas other than just a camera an lenses, such as computers, compact flash cards, additional HD storage, etc. These lens configuration also pertain to the imagery that I like to shoot. There are many options depending on what you are wanting to shoot for yourself. The sensors in all the Canon cameras are pretty great and you won't go wrong with them.
If you're a semi-pro/pro (non photojournalist/sports photog) then the 5DMKII is a great camera if you don't have the funds for a 1Ds MKIII, however the 1DsMKIII takes the crop and is pretty awesome. The auto focus system is way better, along with the more rugged body.
The biggest thing to remember is that good equipment is just the entry to good photography. It's all about your eye and your vision. Just because you have a Mont Blanc $10,000 pen doesn't mean you're a writer. In the same respect, having good gear doesn't make you a photographer. It come down to final product that you are outputting.