I've had my x for almost two months now. I've tried all different things, but what's worked wonders for me is simply turning the phone off once a day. I'll throw it on the charger from midnight until about 6, obviously its fully charged at this point, but I then turn it off, leaving it plugged in, and get ready for work. Pull it off the charger and turn it on as I head out the door.
When ever I have done this I get between 22-39 hours. I've gone a week where I do not turn it off and the battery is good for 14-18 hours. this is my first android phone, so I'm far from an expert, but I think turning it off helps to close any programs that may be running in the background.
Give it a go for a few days....couldn't hurt, right?