I am and will forever be a Nikon guy. Unless you're rich enough that you can just throw money away by the boatload, with DSLRs you put yourself permanently on a Nikon or Canon path with your initial decision because, before that first "entry level" camera goes the way of all flesh you are deeply invested in lenses and other items that are not compatible with the other brand. A lot of those lenses cost a lot more than the camera bodies.
(Yes, I know there are Sonys, Pentaxes, and other DSLRs out there, but Nikon and Canon dominate the market above the entry level almost to the exclusion of every other DSLR brand. Until you get up into the larger formats you almost never see a professional photographer using anything else.)
I'm a Nikon guy because, although there is a bit of a price premium, their lenses for the most part stand head and shoulders above Canon's, and at the high end their cameras leave everything else behind.
Their base entry level camera, the Nikon D3100, is a good little unit, but for a little over $100 more you can get a D5100, which is a spectacular item (particularly for the price) with much more capability and versatility. It might prove to be all the camera you will ever need, both for your initial foray into the field of DSLR photography and after you progress to near professional level. It doubles as a highly capable HD video camera as well.
Nikon just released the D8000, which is being marketed as an amateur camera but is quite a bit above entry level in both capability and list price. It makes me drool like I do when I visit a Porsche dealership.
I bought a true entry-level Nikon D50 many years ago (right after it was introduced) and I still use it extensively, although I now have enough lenses that I can't carry them all with me anymore. They don't make that model anymore -- the D3000 is still available, though, at startling low prices.
I wouldn't go the micro 4/3rds way myself. Tastes differ, but the whole point of a DSLR is the unlimited horizon for growth as a photographer, and micro 4/3rds units are much more limited in the availability of lenses and peripherals, and their prices tend to be even higher than entry-level DSLRs.