I have a home-brew 12v set up - my rear light is an orange xenon strobe - the kind used in home security systems. Got it from an electronics shop for $20. You can see it a kilometre off - brilliant in foggy weather. The other day a car pulled over and the driver, a keen cyclist he said, asked where I got the fantastic light from.
A good alternative if you're in the US is
http://www.swps.com/ligcombikstr.html - a Lightman Commuter Strobe.