Ah, that at least tends to be affordable, since for that you don't normally need a long lens unless you're going papparazi-style, or shooting from the back of a crowd.
One note: -most- DSLRs use a smaller sensor than the more familar 35mm frame. So if you're looking at books of film photography and noting what focal lengths show up, or finding rules of thumb there, you'd want to adjust things slightly. Ex -- a Canon 50mm f/1.8 casts an image circle of a given size (or, perhaps, a rectangle within that image circle if there are internal baffles), but if you use it on a Canon 300D, the small sensor results in a crop similar to that of an 80mm lens on a 35mm system.
For street photography, you'd probably want a pretty short-to-medium telephoto; many 'kit lenses' cover this range reasonably well, if usually with slow apertures. An f/1.8 prime (or an f/1.4, but that's usually more expensive...) would let you use a very shallow DOF and might make night shots a bit easier, since you could get away with a shorter exposure time.
I'm not too familiar with the Pentax line-up, but they've gotten good marks for quality viewfinders, and lately they've been pushing some apparently pretty good deals including bodies with image stabilization tech already built in. It's going to be fairly hard to go wrong, 'tho, unless you add more requirements.
I use an Olympus E-1, which is very nicely engineered, but a bit long in the tooth and not the best pick if you'll be using ISO 1600 a lot, or if you want a fast normal lens. Perhaps the uglier bit is that there's no image stabilization yet, unless you pony up for the new Leica lens.