It all depends, for now you have fish only. Do you plan to get corals? If you stay fish only, than you don't need much light. If you are planning on a reef tank, than I believe that 5 watts per gallon is recommended.
I have a 46-bow front with 192 watts PC lighting. My tank is pretty much FOWLR, except for a small frag of Xenia. 192 watts puts me at about 4.1 watts per gallon. My xenia seems to be doing great, but for the more delicate corals, you will probably need at least 5 watts/gallon.
If you decide that you will need allot of light, look into VHO or MH lights.
If your keeping fish only, then any light fixture, like the one your tank came with, is fine
:happyfish