I personally prefer Canon over Nikon. They are practically very closely matched. Canon is what I personally picked considering some personal research and beliefs. I even liked the name more.
What "engineersnitk" said about Canon being Mac, and Nikon being Windows is totally inaccurate. Other than IN-CAMERA image enhancement edits, the Nikon brand has nothing more to offer. IF you know nothing about Photoshop, Lightroom, or any Image Editing whatsoever, and you are going to use Straight-Out-Of-The-Camera JPEGs then go with the Nikon. If however you intend to use your camera's full potential, shooting RAW format, and editing your shots, in Photoshop, then all the "in-camera" goodies, are skipped for a finer and more precise procedure done by Photoshop.
Example: YES, there are some great noise reduction features in some cameras, but have you ever tried Imagenomic's Noiseware?
Other than that, basically at the same price range you are looking at:
Nikon: Slightly Better Noise performance for the Nikon due to slightly newer sensor technology. Some more MegaPixels to play with.
Canon: Slightly Better Autofocusing / Metering mechanisms. Slightly Better User Interface and Ergonomics. As a Noob, I could use a Canon 1 minute after I picked it up. That's not the case with Nikon. Plus Canon is also known to be Tougher.
( Plus although they are quite close, Canon's Glass is superior. )
PS. As for the lens, if it's your ONLY lens, DON'T go with a 50 1.8. Using a Crop Sensor camera ( which you intend to buy ) the 50 will act as a 75-80mm. That Focal Length is not suitable for everyday photography, and almost forbidden for indoors. Plus the Sharpness of these cheap 1.8's wide open is retarded. I DO OWN a 50 1.8. My suggestion would be this: Go for the Kit 18-55, AND a 50 1.8. You can do great portrait, video or low light photography with the 1.8 but it WILL bust your nerves if it's your only lens.
PS2. If that's any worth, I have used a Nikon 3100 in the past, and currently I own and use (daily) a Canon 650D. I got more than 100K Clicks, so I can assure you that is a good camera.