What do you want to do with your tank? Do you want to start slow with some easy plants and a low-tech tank, or do you want to dive right in and try a high-light tank with injected CO2 and a fert regimen?
For a tank in the low to medium light range, a two-bulb T8 shop light or a Marineland Double Bright LED fixture would be good. The shop light is cheap to start. The LEDs shouldn't need to be replaced and use less electricity. Pick your poison.
If you want to step up to a high-light tank and you've got some DIY skills, I'd strongly recommend that you consider building an LED fixture. I built one for my 20H and I'm growing high-light plants while using 30W of juice.
If you're not the DIY type, a four-bulb T5HO fixture or a Marineland Reef Bright LED fixture should do the job for a high-light tank.