Actually, I am working on a lap timer... mainly for myself, at least right now. I have two versions, one with a row of LEDs that is tough to figure out and a new version with a small LCD on it (haven't tried the new one on the bike yet). It has fastest lap, previous lap, current lap, and total number of laps displayed at the same time. On the one I am using now (the old one) I have a button mounted on the case, but I want to get another kill switch mounted on the other side of the bars and hook that to the timer. They are both designed to mount to the bars with a little clamp like perches have.
It's cool to see that there is interest, maybe at some point I will be able to produce them... right now I am working on something else. It is also a timer, but not on the bike. I designed it for a friend who was doing timed running for baseball tryouts and practices, but also to use on their MX track, like timing turn or start speed (it isn't set up for laps). It uses two infrared receiver/transmitter pairs. I have been working on getting to a point where I can produce these, way more work than I ever imagined! If I get to the point where I'm selling them I'll post in the new products forum.
Andy