Hey, im back, after now finally buying my camera. Instead of the olympus e620 i was looking at earlier, i decided to go with a Pentax K-X with a 18-55mm lens. I bought the camera with just one lens to get accustomed with the camera and make sure it was the right thing for me, and, before i start going on vacation again, i wanted to get a longer lens (for wildlife or far zoom shots). I was going to buy a 55-300mm lens with my camera, so i was hoping to get a 55-300mm lens, or a 70-300mm third party lens, or something quality.

When looking around for a lens, what are some guidlines i should follow? I dont want to buy something too expensive, but i also want something thats compatible with my k-x. What are the normal checks i should do when buying a new lens?

Thanks in advance.