It'd be tank mounted arms, right now I was looking at a rather cheap fixture (329) from Aquatraders.

http://shop.aquatraders.com/Odyssea-...HO-p/54231.htm

OR

http://shop.aquatraders.com/Odyssea-...ct-p/54205.htm

Which, while a bit longer than my tank needs, can be used on the future tanks I purchase. My current ballasts have a bit of rust on them, and the fixture is a bit bigger than I want. Also, 48 will cover my future tanks ;)