So my family and I are planning a trip to yellowstone this summer. I have a D90 with the 18-105 and a 35 mm f1.8. I am thinking that I need a telephoto will be needed, so the 70-300? Is a good choice? Also I am thinking used from a place like KEH. (Going for $350 now). Or does anyone have a suggestion on another brand for something similar in that price range?

A wide angle also has crossed my mind, I am thinking that the 18 mm will be enough.

Any suggestions?