I don't overdrive the bulbs, but this is what I do to a shoplight: (this is for a basement fish room)
I try to get old crappy ones for free. I don't care if they work, just so they're not too rusty. Freecycle is a possible place to get them, but if you see any out on trash day that works too.
I get a 2-bulb T-8 electronic ballast from a home store. I've been paying about $20 a piece for them. I screw the ballast to the top of the fixture, usually drilling a couple holes to run the wires inside the shoplight, and wire it up to match the diagram printed on the ballast.
In cases where I want a 4-bulb light, I get a 4-bulb t-8 ballast, and use a couple strips of wood to attach the two shoplights side-by-side. A 4-bulb shoplight is pretty close to the price of a 2-bulb one!
At the very least, this probably saves a lot of money on electricity over the old crappy magnetic ballast, and the t8 gives more light than an old t12 bulb. I would guess that the bulb life might be longer, too.
Lobo's idea of using a vent pipe for a reflector is a good idea. Getting a length of white aluminum gutter would also work- I will have to try that for compact bulbs if I can find double sockets. You probably don't need a socket with a switch on it (if you can find one without), because you're probably going to use a timer.
