Jeremy,
There are a lot of awesome new 4strokes out there...but word of warning if you've been out of things for a while...it seems the new breed of 4strokes require rebuilding at least as much as the 2strokes, if not more in some cases. If you want a reliable and long-running between rebuild type of 4stroke, you need to look at bikes like the XR400. It is heavier and does not have as much power, especially at the top end as the new CRF450s, but it has the old bullet proof engine.
If you consider 2strokes, look at the Kawisaki KDX200or220 or the KTM 250or300 EXC. They are tamed for the trail and have plenty of low end grunt. Also, I think it is cheaper and easier to rebuild the 2strokes than the 4strokes when the time comes. Unless you are racing or riding every single day, you should be able to get 2-3 seasons of riding in on a KDX before a rebuild. That's pretty cheap entertainment.