I rode a tw for my motorcycle safety course and I really liked its manuvering and riding position. I like the fat tires they come with. I can vouch for suzuki singles, I have an old DR125 that is just a trail bike, but they also made an sp125 enduro version. That bike is bullet proof. It sits for years at a time but always runs great with a minimal amount of effort.
I love the new DR200SE because it has a three gallon tank and gets excellent mileage, but I hear it's not super-capable off road. Also, many these small displacement bikes have a very seat height. Unfortunately, it seems bikes like these are mainly intended for beginners. If you're tall, or want better off road capability look at the Kawasaki KLX250 or Yamaha wr250R.
Look at advrider.com, there are some great dual sport discussions there, tons of info. Good luck, I wish I could be shopping for a small dual sport as well!