just got a canon 5d iii - what lense now?

Hello everyone. So I decided to splash out a new 5d iii. now I need some help with lenses.

My previous camera was a canon 550D with a 18 - 55 mm canon efs lens. It pretty much served me well. My first question is the following: I understandt that the 18 - 55mm range is different for a full frame sensor to the sensor in my 550D. SO what would be the equivlente for a full frame sensor. The reason I ask this is because that lense served me well. The reason I decided to go full frame is to get better quality so I can print large the pics I take so I would like some nice quality lenses to get the best of the camera.

Thanks everyone