Apologies for detouring this thread...
What I wanted to say is that choosing Nikon or Canon would not be too far off the mark. But Pentax, Olympus and Sony does have their own system advantages that some might be attracted to, so don't discount them up front.
If you ask me, small and light goes to Pentax matched to it's pancake lenses. A K200D is pretty cheap and have stabilized sensor to boot.
Entry system DSLR currently goes to Canon 1000D/450D for pricing. Want Nikon? Maybe wait till Christmas, Nikon is likely to announce update of their entry level system this September. Basing on past trends, they (C&N) tend to leap-frog each other with subsequent announcements.
Not much into Oly or Sony cuz so far their lenses and accessories are somewhat relatively more expensive.