would be the most economical option. A lot of people (me included
) really like t5ho lighting, but it gets a little more expensive.
You could use this fixture and one of your existing fixtures to add a little bit of extra wattage, and that would get you around medium light. (what fixtures did it come with?)
My guess is you will probably want to ditch the current lid/hood setup on the tank, and just get an all glass top. This way you can just put your new fixture up on top of the tank.
There is also the option to get a retrofit kit and install some different lighting in the hoods you already have. That will require some electrical skill (not too much). Really for the price though, it would be tough to beat the fixture linked by swerner.