The lens wonks around here will want to know what you want to do... shoot wildlife? Sports? Portraits? Indoor? Outdoor? Candids? Will you be using a tripod or shooting mostly handheld? Do you need a 300mm zoom? 400? 500?
Many people recommend the 70-200 f/4 L -- it's a nice quality "L" (meaning "luxury") lens with good glass, with a decent amount of zoom range that's not TOO expensive.
For Christmas, I (also a Dig Reb newbie) got a Tokina 24-200 (I think the model is called 242AF)... it's fairly fast, well built, sharp, and a good multi-use walk-around lens. But I wouldn't want to shoot sports (not a super fast focuser), nature (not enough zoom), or low-light (not a "fast" lens -- meaning rather bad maximum f-stop)situations with it.
Give them more info, and the opinions will flow!