Grum, Canon deffo has the edge over Nikon in terms of overall range, although I think most people would say there's nothing in it in terms of quality when you're taking a close look at the pro-level fast glass. Nikon is more expensive as a whole thoug by a whisker.
D300 is a great buy. I had a D200, which shares a very similar body, and the handling is superb. The D300 is better in terms of high ISO and AF though, which makes it a very enviable camera.
With regard to DX-format lenses, you aren't limited to AF-S (built-in motor) lenses that are designed for the like of the D40 and D60, those models without a body-based AF motor. I have a D2x and like the D300, you can use 'D'-type lenses, Nikon's older generation of glass from its 35mm film camera days. The AF-S lenses with built-in motors are quicker mind, but the fast glass (70-200mm VR etc) is expensive compared to the D-type versions, although most offer the best quality with a very wide scope of use.
A typical example is the 70/80-200mm f/2.8; the AF-S 70-200mm f/2.8 VR retailed for £1,100+. It focusses faster and has VR. The 80-200mm f/2.8 doesn't have a built-in motor so focusses slightly slower but is fairly equal optically, but no VR - that retailed for about £700.
The one thing about Nikon is there are none of those 'halfway house' lenses like what Canon has; no 17-40mm f/4, no 70-200mm f/4. But then again, for me, that was a conscious decision because I felt that cameras themselves offered more than what Canon did at the time and I'd make the compromise by paying more for glass
NB: here's how the Nikon glass works:
AF-S: has a built-in motor so can be used on all Nikon digital bodies
AF-D: no built-in motor so can only be used on bodies with motor (D200, D300, D3 etc)
DX: Digital-only (1.5 crop) bodies (all bodies bar the D3 series and the D700)
G-type: No aperture ring
VR: Vibration Reduction
Think there are more but can't remember them at the moment...