I bought a 125 gallon today on sale at the lfs,

Congratulations! A 125 is a nice size for plants, IMO. Six feet long, 18"
wide, just under 2 feet deep. With this size, you can use just about any
lighting you want. Though, price-wise, flourescent tubes might make the most
sense.

Are you getting a compressed CO2 system for the tank, too? If not, it's
probably best to keep your lighting levels down at around 2 wpg. 125 gallon is
sort of large for DIY!

Leigh

http://www.fortunecity.com/lavender/halloween/881/