A mercury vapor bulb (MVB) will provide light, heat, UVA and UVB. It's an all purpose bulb. They're pricy - I think I paid $45 or $50 for mine. The UVB they put out is more intense than what you get with a flourescent bulb.
Here's a link with some products:
http://lllreptile.com/store/catalog/rep ... por-bulbs/
The Powersun and T-Rex bulbs are MVB's. The kind you'd use for an aquarium are the flood lights, not the spot lights. The spot lights are just much too strong.
There are special considerations with MVBs because they are so hot and intense.
1. They are not suitable for aquariums under 55 gallons.
2. You need to use a ceramic light fixture.
3. And, the distance between the light and the basking spot is very important because if you get the bulb too close you'll overheat or burn the turtle.
If you've got these considerations covered, then I think they are great because they put out stronger UVB and they are all-in-one.