How long is your tank? If it is 48" or more, throw out your canopy and get one that fits the tank. If I understand correctly, you use very short bulbs, so only the center of the tank is lighted sufficiently?
For a 48" long tank that is 24" deep, there are many choices. You can go the T8/12 road, which gives you about 130-160W, which in combination with excellent reflectors (?) would be considered low light, but allow you to grow a lot of different plants. You could overdrive them, which would increase the intensity by about 50%, getting into a range where you can grow more demanding plants.
Or you use the T5's mentioned, which are brighter than the "regular" fluorescents, and due to their diameter are more efficient with a suitable reflector.
To go the high-light route, you should check out PC's like from AH Supply. This is a little more costly and gets fairly hot, but you get a lot of watts and good reflectors so you can grow the ever famous Glossostigma :mrgreen:
I don't see much advantage to VHO lights, they are expensive, get very hot, are not so efficient (lumen/watt), and overdriving NO bulbs gets you the same light for less.