Please keep in mind opinions on this information is widely available across this site, and it's always appreciated when members do a bit of research on their own and then ask more specific questions or ask for opinions on specific bulbs. It can also be more helpful to you instead of people spouting off various names, strengths, and sizes.
Arcadia bulbs are typically considered the best on the market, though they are more expensive than others. They are also currently only available from one place in the US. I would recommend either of these two options:
I prefer the second option. I recently upgraded my own dragons light to the double bulb fixture and it changed his personality immensely. He is so much more active and his colors are incredible now. He is always bright and happy with the increased UVA.
The two brands recommended are the Arcaida linked above and the Zoomed Reptisun 10.0... if you are outside the US or UK then you might need to start looking into other brands. Having used both brands, I like the Arcadia I have but on a budget would be just as happy with a Reptisun and it is about half the cost.
The lighting guide on this site is sortof out-dated. Its a much less expensive setup, but it is not as bright or as strong. If you at all can get a T5HO lamp and fixture that will be your best bet.