I've been looking into the same things myself, I have to tell you that the best resource I've found where many people debate these same issues, on a daily basis, is Adventure Rider. You can find them at
http://www.advrider.com. I use the thumper forum as that's where the guys & gals with the singles gather.
What I've found from my research there is that a
DR-Z 400S with a few of it's brother the
E's pieces-parts will make it an amazingly capable on/off-road machine. It's light, powerful and has tons of after-market stuff available for it. Additionally, there are always used ones around and I have fantastic support for my Suzuki's.
Time will tell and the only thing I'm waiting on is the funds. Saving the pennies! :-)
Make sure you stop back and let us know what you decide!