If you want to go DSLR with IS, then skip the kit lens for a Canon or Nikon and just buy an IS lens right away. If you want to save a little money and get IS, then go with a Pentax, Sony, or Olympus b/c their newer models have IS built in the body so it works on every lens.
Nifty Fifty is just a nickname people have given Canon's 50mm f/1.8. It is a prime lens meaning that it has a fixed focal length. The wide aperture on it allows it to give you a faster shutter speed. It also allows for a smaller depth of field when you need that. The downside is that it is a fixed focal length and the restricted depth of field when you do not want it. Pretty much every brand has a similar lens. Nikon's is also inexpensive, but it will not auto focus on a D40. The Pentax model costs a little more, but it is also a little faster at f/1.4 and has a more rigid build quality. I am not sure much about one for a Sony, but even if they do not offer a new one, there are sure to be used Minoltas around that work on it. I believe the Oly (4/3 system) one is pretty expensive. I do not believe that anyone offers an IS prime lens, so if you want it on one of these, you would need to get a body with IS.
Kevin