I have 2 of these on my tank.
http://www.apc.com/resource/include/...ase_sku=AP7900
They are meant for remote power control of servers. But, for me the fit the purpose, and I got them cheap. They have 8 outlets that are controlled independantly, and a network connection with a intgernal web server. They also have a digital amp. display and log power usage and run time of each outlet.
So, I know how much power I use, how long the heaters run and a real simple web interface to set the timer schedule. Heck, they even have over current protection that will shut down a single outlet if it starts drawing more power than you program it for.
I know the APC units new are expensive, but there is a few other brands with 8/16 outlets for about $120. For me, these were cheaper than 16 timers as I got them as demo units for one of my server rooms.