Blenders for smoothies

Alton Brown/Good Eats had an episode on smoothies and what to look for in a blender. I would recommend starting there. I personally have a 1100 watt ninja blender and it does what I want it to do and it was a little expensive(about $100). I have had about 3-4 $25-$35 blenders and have had them all go shortly after buying them. Some the store replaced some didn't so I decided to spend a little more and the ninja has lasted about 3 years so far and is going strong.
Now if you have an inexpensive blender and its doing you good then by all means stick with it, and don't purposely try to break it, by overloading it, so you can justify buying an expensive blender.

Vitamixes are great... for professional cooks who want to be able to make hot soup in a blender because the blades are powerful enough to heat the liquid to boiling through friction. And yes, it will destroy ice/whole veggies/whole fruits (maintains the fiber content). Also makes fantastic instant ice cream (pain to get out though). I feel like for most people a $100 blender is enough though.

Carafe won't fit in your average fridge and the plunger thing is kind of silly (works, though). Blendtec's shorter carafe is a nice selling point. Those are the two top options if you want the best of the best blender.