Canon Rebel vs Nikon D300?

I'm looking to buy a camera and would like to know which you would prefer and why? Thoughts, comments, and personal experience would be great!

Are you sure that you're having the D300 in mind, not the D3100 or D3000? The D300 and its variant, the D300s, are the professional grade crop frame cameras in Nikon's lineup, costing $1700 for the body only, without a lens.
The Canon Rebel is not a single camera but a whole series of cameras, which all belong to the entry level segment, randing from $500 to $800 or so. These are not comparable to the D300s at all.
Now, if it's between the D3000 or D3100 and the Rebel series cameras, then that's more meaningful. There it basically boils down to personal preference entirely, both are fine. If you're on a tight budget and wish to take lots of portraits, then Canon may be the more economical choice, as it has a cheap "portrait lens" available, whereas the entry level Nikons would have to use a $200 more expensive lens or forego autofocus on the cheap portrait lens.
Also consider the Pentax Kx or Kr.

The Canon Rebel is an entry level camera, the D300 is a semi-pro model.
I presume it was a typo & you meant D3000, which was an entry level camera by Nikon - it's now superseded by the D3100.
Both are competent entry level cameras - you're best off trying each one out in a camera store. What feels better for you (in terms of weight, button position, menu choices) might not be what I choose.

You should buy this one Canon EOS Rebel T1i
Specifications:-
+ Great/Easy to use - User Interface
+ HD Video
+ Live View
+ Amazing Image Quality
+ Comprehensive Software Package
+ Large Variety of Lens options
+ Performance
+ Obviously, Cost
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