The HKS Type 1 Turbo Timer has a 2 stage shift light as one of it's features. It is easily adjustable, and makes a noise also when you hit the limit you've set. Great value with it's other features for $300 (if you want to spend that much). I understand you can also get shift lights that hook into the cigarete lighter. Haven't had any first hand exp. with these, but they wire into a control module, where you can manually adjust the limit. I think Autobarn sell them. I've seen one wired into an S15 - looked pretty damn sweet. The light itself is small, and easily concealed.
Good luck
46n2