Scott....I've owned nothing but Nikon, so cannot compare to anything else. Started out with an F3, 8008S, N90s, F5 (still own that one), and a couple of years ago moved to the D200 w/18-200 lens Craig mentions, verticle grip, extra battery. I have actually sold a few things over the years to collectors, interior decorators, etc. I have a backpack (plus some) full of Nikon gear. The great thing about Nikon is they never change their mount, so you can take an old (but excellent) 50-135 AIS lens and stick it on the new body...you'll lose some of the wiz-diz features, but the lens will still work if you know how to expose manually. The 18-200 came with a "kit" I got from B&H out of New York...it's not a cheap lens, but will cover pratically anything you'll ever shoot, has good glass, vibration reduction...all the bells and whistles. Even the pop-up flash on the D200 does a decent job within it's range. I'm very happy with that combo for general shooting, and it will all fit in a smallish camera bag (I like Lowepro bags). For 90% of my shots, that's all I need...when I get real serious, of course I use a Gitzo Carbon Fiber tripod with Arca-Swiss Ballhead. I haven't looked into the D300 (I'm afraid I'd want one). I tend towards the "Pro" cameras because I'm used to having the control they give, and I won't own an SLR without depth of field preview. I shoot mostly macro and landscape type stuff, so the pro features are a necessity for that type of shooting.
For my "pocket camera", I have a Sony W-7...nice, sturdy little camera...7.1 MP...Carl Zeiss lens...great for general shots, and has one of the more powerful flashes for a non SLR.
Here's a macro shot with the D200 and 18-200...this was hand held...not serious work, but just an example of something I'd normally have to shoot from a tripod. It's not perfect under a Loupe, but not bad sharpness for hand held in low light with just a "kiss" of flash.