I use Zymol cleaner wax on my truck because its cheap and you don't have to let it dry so I can do my truck in a bit over an hour. Seems to last 3-4 months, I last did my truck in late June and I'm noticing water is starting to stop beading on the hood and roof so I'm due for another coat.
http://www.amazon.com/Zymol-Z503-Car-Cleaner-Wax/dp/B0009JKIRC
2-3 times a year is about as ambitious as I get these days with waxing.