few options:
don't worry
or
bury the tank below frost depths
or
insulate the tank
or
install a heater

I'd recommend bury the tank.

Barry,

I'll bury it. There was one buried under the Michelle Kaufmann house here at the Museum of Science and Industry. I don't remember the manufacturer.

I'll insulate it. Heating it wouldn't make much sense in terms of saving energy. (Or maybe it would. I haven't done the calcs)

I need it to be above the spout on the outside for gravity to move the water.

Does that make sense?

Thanks!

Burying it while relying on gravity for pressure sure doesn't make sense... am I just reading that wrong?

It's a patio so the top surface is 4' above the ground.

The spigot could be on the side 12" above the ground.

Maybe I could put it into the basement?

But that doesn't help.

I need to think about this some more.

you mean a cistern?

yessir

arent some of them already pre-insulated?

This is cool:

http://www.uaf.edu/ces/publications-db/catalog/eeh/HCM-01557.pdf

Anyone know of a manufacturer?

Landscape irrigation probably isn't a huge deal in freezing weather since many plants are dormant during this period. But if you do really need it, you might look at Steve Baer's device for maintaining free-flowing water in stock ponds and tanks:

http://www.freepatentsonline.com/3618569.pdf

You know, physics and whatnot.

why not use a pump?

we had a client retrofit an aquarium filtration system into his house and one of the components was a buried tank that had a pump. might want to look at ow they do the filtration and water storage for large aquarium systems...