I've got a planted 38-gal tank, and I use two 20-watt striplights. One's a "plant grow fluorescent" I got at Lowe's for about $6 (real high in the blues and reds, dim to the human eye) and the other is a "Sunlight" bulb (by GE, I think) that puts out 5000K. I got it at Walmart for $6, but some hardware stores had it for $9.
I like them really well.
-- Pat