It seems that you are looking to buy something in the $600-900 range.
If this is your first DSLR, I suggest either the Nikon or the Canon, not only for their ease of use, but because they are the most popular.
However, the newest Nikon is the D90, and its major benefit is the ability to record High-Definition movies. This is great, considering none of the others have that feature. Canon's T1i, which comes out early May, will have Full HD movie recording and should be $900 with lens. So if you can wait until May, then I'd get the Canon. If you can't wait, try out the D90. Also, the T1i will have the same sensor as the mid-range 50D ($1400 MSRP) which means performance will be quite speedy.