I put together this logic probe circuit the other night based on this project...
http://www.talkingelectronics.com/projects/100%20IC%20Circuits/1-100_IC-Ccts.html (about halfway down the page).
I built it inside a sharpie like pen from the dollar store, and I already had the parts on hand. It seems to work just fine and the cost is only 3 or 4 bucks. I will be using it to trouble shoot an Mpu i'm having problems with.