Object distance sensor?

Hi, I'm looking to make a project which would involve detecting an object, and knowing the distance between the object and the detector. The distance will be on the order of 5-10 cm, and I would like the object to be any of a variety of objects, perhaps as narrow as a pencil. Are there any good arduino sensors that could do this for me? I don't actually need the precise distance, but I do need to be able to look at a signal and tell if the object is getting closer or farther away.

just check distance sensors e.g. at - http://www.sparkfun.com/categories/139 -