Being a Nikon user for over 15 years now.. I have an affinity for their products. However, if you really have no real pro level gear already, Canon and Olympus have some really really nice stuff. If the "live view" via the LCD is important to you, then I would recommend either the new D300 from Nikon or the Olympus Evolt 510. I think the Live View is the next big thing that all companies will scramble to include on their consumer DSLR's... not a bad idea for the hard to see shots and unusual angle usage.. and really helpful to for tripod framing,etc.
The 510 is a entry level but will run you around $600.. the D300 is an advanced level camera and runs almost triple at $1600 of so... So, I'd recommend the Evolt. Both are 10mp so you have lots of room for cropping. Both have sensor cleaners which is another "must have" addition to today's cameras.. I really like the Nikon.. but then again... I have 10000 worth of Nikon lenses so it makes sense to stick with it.
Anyway.. I'd do some research and see what folks are saying. I don't like dpreview forums any longer (they have gone waaayyy downhill).. but the reviews are still complete - see here:
http://www.dpreview.com/reviews/olympuse510/page31.asp
Good Luck!