Basically Milkshape or Blender.
Milkshape is $25, and is rather basic to the point that I don't see much use other than low-poly Blockland models.
Blender is free and easier than Milkshape (my opinion) and has many additional features if you decide to do things other than Blockland models.
Don't know any good Milkshape tutorials, but Blender tutorials I'd recommend are
here and
here though they may not be updated with the new UI.
There's a few others such as Sketchup and Wings 3D, but I don't know prices and if they can export to DTS