I got sick of lugging around Nikon, so I switched to Olympus E-P1 at that time and never looked back. Recently, I upgraded to the E-P3 and it really does have the worlds fastest auto focus system as advertized, plus it's touch screen like an iphone. The size of the camera, and ability to change lenses makes it the perfect travel camera.
If you're not buying a full frame sensor Canon or Nikon, which typically run in the $3-4000 range, there is no advantage in using any of their cheaper DSLRs since they are cropped sensors as well. For less than a $1000 you can get a 12MP camera with 14-42mm lens, and 45-150mm lens. The Olympus micro 43 sensor is 2x crop, so the equivalent focal range would be 28-84, and 90-300mm. There is no way you can find any other DSLR that will match that focal range at that price. Olympus just released the E-PM1, which is cheaper smaller version of the E-P3, but I highly recommend the E-P3 for the touch screen.
Sony is releasing their NEX7 24MP camera soon, which looks awesome as well, but the sensor is 1.6x crop, so the lenses are a little bigger and more expensive. The new Nikon J1 has a 2.7x crop sensor, but it will retail for over $1000. Canon does not have a mirrorless interchangeable camera yet. Another nice thing about Olympus micro 4/3 cameras is Panasonic lenses will work since they are micro 43 as well, and you can buy adapters for nearly any lens type.