They do make LED replacements for incandescent lamps too...
For example: Digikey page
The type of lamp you are looking for is called a festoon.
Here is a site that has just what you are looking for: Automotive Festoon Lamps
Here is what I do. I buy batteries from this guy all the time:
All-Batteries Outlet
Now with these I build my own battery packs. They are rechargable which is great. If you don't wan to build your own packs, they also sell pre-assembled packs.
Preassembled 12V pack
I also picked...
No need to bring in a second 12V line. Just connect the switch around the resistor. Current will take the path of least resistance and the resistor will be ignored when the switch is on. When the switch is off and the path is broken, current will move through the resistor.
Microcontrollers I got. That is kind of what I was thinking. The project I am working on already has two basic stamps in use. I also have a drawer full of 16F84's which could be used. Was thinking a simple clock circuit could be used if I could find the respective pins to use...