I made one of these
http://www.pc-workshop.net/slurp/index.shtml
Of course mine is a little different. I used RED and green LEDs, put in a back light so I could see it at night and nicks the front a little with a dremal.
One thing though, buy at least one quality thermistor, the kind they use for measuring CPU temps on some Socket A boards. RatShack ones suck. I had to toss one because it consistantly read 10C over the others. Meanwhile another shattered. Not to mention they are too big to fit near the CPU die.