Dwarf hollies, Hemlock, Mugo pine, Dwarf white pine (there's a long list of dwarf pines), arborvitae also has some dwarf cultivars, globe-shaped japanese cedar, any number of junipers- there's a seemingly endless list. Out of all of those, the junipers are propably going to be the least expensive and easiest to find.

Twelve inches tall? If you're thinking about shrubs, you'll need something with dwarf in the name! And be prepared to trim it at that. I was going to recommend Ilex glabra 'Shamrock', but even that supposedly gets 2 1/2 feet tall.

Here's a link from North Carolina with a chart of small shrubs. I've seen dwarf azaleas at work (mentioned in this table) and they truly do not get very tall.

Here is a link that might be useful: Small shrubs

Iberis -- perennial candytuft.

Nell

You could do Bill Wallace lorapetalum if you don't need actual green but just "evergreen." It is no more than 1 foot tall supposedly.

Oh I forgot... Boxwoods.

Gardenia radicans is a low-growing form of gardenia.

Candytuft gets quite thick in the sun and makes a nice low growing hedge. My radicans gardenias are about 20" tall but are really great plants.
I like both those ideas.