You already picked the cameras I would have suggested to you. However, there are also the entry level Canons (see below).
Get one of these with the 18-105mm kit lens, or body only (and get something like a higher quality zoom or the 35mm prime as walkaround lens)
Not the 18-55mm kit lens, because (a) it has a really bad manual focus (and manual focus is already hard enough with these cameras) (b) in many situations, it just doesnt have the range one would want.
If you want maximum quality for a cheap price, a prime lens (like the AF-S 35mm f/1.8G DX, as I use it) is the way to go. Zoom lenses havent been invented before the 1950s and havent been in common useage before the 1970s. People have been photographing long before that point. Just zoom with your feet instead of with the lens. About 30mm on DX (and 45mm on full frame) is the "normal" focal length, which is about as wide as our eyes. Thats why this is the most general focal length.
You might also want later to get (depending upon what you want to do):
- a telezoom (like the AF-S 55-200mm VR DX, which is the cheapest and lightest of all telezooms and the picture quality is also great except maybe the far end; however it is very plastic, so treat it with care or get more expensive and heavy models)
- a wide zoom (like the AF-S 10-24mm DX) if you like landscape or really "close to the action" photographs
- a macro lens if you're into flowers, insects and stuff like that (for example the micro-Nikkor AF-S 85 f/3.5 DX) (*)
- prime lenses for low light / portrait / other bright light/shallow depth of field applications (like the AF-S 35mm f/1.8 DX, the equivalent to the traditional 50mm normal prime lens used for street photography and journalism).
- Also always check out the concurrence for good, cheaper alternatives to Nikon.
(*): do not expect to be able to shoot sports with macro lenses, unless you can disable the macro part, such as on the awesome Sigma 105mm F2.8 EX DG OS HSM (a very expensive but also very high quality macro lens). Macro slows down the autofocus very considerably.
Oh, and:
- flash (like the fb600, ca $200)
- tripod (dont get cheap ones for your expensive camera; for example, Manfroto or Gitzo are good companies)
- remote (thats very cheap and can be very handy)
- later filters like polarization, grayfilter, UV etc (but get high quality ones like Hoya Pro1 so you dont get scratches on your lenses from broken filters)
Get the D3100 if you want to spend the least amount of money. Obviously its a tad outdated with the sensor and the monitor. Otherwise its perfectly fine.
Get the D3200 if you really want maximum resolution.
Get the D5100 if you want best low light performance and highest dynamic range, as well as a bit more "professional" interface (but not much, the real upgrade in this respect is the D7000). Personally I also choose it because I absolutely wanted a full featured swirvel monitor.
Both Canon and Nikon have a huge selection of lenses, and are leading in the field of SLRs. If you want cameras without shortcomings, one of these two are the way to go.
Canon vs Nikon: this is an old debate. Canon in general strives for more "beautiful" pictures, and maybe a tad nicer user interface, while Nikon traditionally always tried to be the sharpest, most performant etc.
Either of them can make great pictures. Just get into the shop, hold them both in the hand and try them which you like better. Once you decided which system you prefer, you'll be bound to it, so dont take this decision too lightly.
Also be prepared that Canon vs Nikon is kind of a religious battle between photographers in the forums.