I would just go out and buy a bag of birdseed. The grey-striped seeds are bigger and will probably produce large single flowers (about a foot across?). The smaller pure black seeds will likely produce a plant with more branching and multiple flowers - but the flowers will be smaller (6-8 inches across maybe?).

Both types would likely get around 6 feet tall.
You can't be absolutely sure what you are getting but when have you ever seen an ugly sunflower?

You can always spice up the row with a few seed packets of fancier types, just make sure when you plant them plant them thick. I think rabbits like to nibble off young sunflowers so you might end up losing a few.

I'm excited. I think I want a sunflower hedge!

I'll second that. Birdseed sunflowers are great for large plantings. I have always used the black oil type with good success, but I am sure the grey striped seeds would work as well. Grey striped seeds are a little harder to find in large quantities. I would plant lots of seeds. A few won't sprout, animals will eat a few, so it is a good idea to plant thickly. If too many grow you might have to thin them out, but that is a lot better than having gaps. Instead of a single row, I would plant a wider row that would be several sunflowers wide. A two foot wide row (at soil level) would accommodate at least two sunflowers side by side, and would produce a better show than a single-file row, I think.

Something you may want to consider is the Maximilian's sunflower. I planted some seeds a few years back and found out that they are a perennial. Once I found this out I just started digging up and dividing clumps and putting them in out of the way spots to provide a nice back drop.

They are not your traditional sunflower as far as the look of the flower itself. Each stalk will have anywhere from 30 or so blooms to over a hundred. They are about 4" to 5" in diameter and completely yellow.

They bloom later than other sunflowers. I'm guessing it is because the flowers are smaller than jumbo sunflowers so take so much less time to develop. They last longer and are really cool looking once winter hits when they are dried.

A big plus (for me here anyway) is that the squirrels don't seem to bother them...and I have plenty of squirrels here.

I've attached a link to a site showing them.

If you go for the bird seed sun flowers (which I think is great) I would consider scattering bulk wildflower seeds in front and back of the sunflowers. It will give the sunflower seeds and small plants a better chance at survival providing rabbits an alternative to eat. Plus it will give some nice color at the base while the sunflowers develop.

Jim

Here is a link that might be useful: Maximilian's Sunflower

Great ideas! I do have a Maximilian sunflower that I bought two years ago. I brought it with me when I moved last year, so I am looking forward to watching it grow in a permanent spot. I'll have to go down to the big box stores and see where I can get the best price for bird sunflower seed, and see if I can get more than just two types.
Thanks again everyone.