inx3us: If you don't mind pricy ($150), here is another solution.
We use the high efficiency version of these at work. They work very well. They package very nicely since they can bolted directly to the PC/104 stack.
If you want cheap, keep an eye out on the surplus sites. I've found power modules from laptops fo less than $20. You may also find something like this:
This particular one isn't too useful for a car since it nedds a 48v input. Every now and then a 12v input version is listed at MPJA.
Electronics run on smoke, if you let the smoke out they won't work