I'll be upgrading to the 350 Rebel from the 300 soon, too. Currently, I have, as far as lenses go:
17-40 F4 L
70-200 F4 L (not the 2.8 - I wish...)
28-135 IS (Junk, way too soft, no sharpness below F8, but the stabilizer is nice)
50mm F1.4 (cheap, great)
with a 22mm sensor, though, that's not quite enough for wide-angle. The 10-22 is looking mighty attractive, and is a necessity if you don't shoot 35mm. The 24-70 F2.8 L is nice, too, but it's not necessary given my other lenses.
Anyway, I have only good things to say about the Rebel, and Canon digitals in general. Nikon may have their D2X, but they really shot themselves in the foot in the prosumer/budget SLR department by not countering Canon's new 8mp sensor. I had expected them to annouce something to that regard for a while now - but my information is a month out of date; perhaps they've gotten their act together.
Anyway, if you have a collection of Nikon lenses, then go ahead and get the D70 or D100 - at least you'll have spot metering
- but if you're starting from scratch, Canon is the best way to go. At the moment.