I'd go with a single 24" t5ho. Or a dual t5ho if you plan to run pressurized co2 or can hang the light higher up off the tank.
Not the best fixture ever, not the best reflectors ever, and definitely not the best hardware, but they get the job done and for cheap.
http://cgi.ebay.com/24-T5-HO-Aquari...625?pt=LH_DefaultDomain_0&hash=item19c4f74071
40 dollars shipped...kablam.
(people will say you get what you pay for, and this is very true, but these fixtures have a decent track record, and at less than half the cost of other comparable ones, it's hard to say no)
Also with this fixture you may actually have too much light going on, so prepare to cut back on your photoperiod or compensate with ferts/co2, or raise the fixture off the tank a bit.