I can't believe nobody else has recommended the easiest solution of all: cold cathode lights...
http://www.xoxide.com/dual-white-cold-cathode-kit.html
I bought two of these kits for a total of 4 cathode lights for $16 plus shipping. These only require 12V to function and come with adapters that plug directly into one of the power supply molex connectors right inside your computer case. Turning on your computer then automatically turns on the lights.
Mounting them couldn't be easier either. They come with a couple little pieces of velcro you attach to the ends of the lights and then just velcro them right onto the mounting board behind your marquee.
The specific site I linked above is currently out of stock, but just do a google for "cold cathode" and you'll come up with plenty of hits.
How in the world is that easier than simply placing an under-counter flourescent light in?
Mounting my under $10 light took only about 10 seconds longer than it took to screw in 2 screws, and could have easily been done with velcro as well.

Cold cathode is certainly the "it" thing in the build-your-own/mod community today, but it certainly isn't any easier than just sticking a fluorescent light in.
Not to say it wouldn't work just fine, and there are many instances where it would certainly be the better choice, such as in the many small area applications it is most commonly used, but for marquee lighting... It just seems like it would actually be extra work to me, when you could just plug in one long fluorescent.