My experience is in zone 3 so it's different from warmer zones but last year I used verbena as one of my annuals and totally fell in love with it. In warmer climates I think it's perennial. I also like portulaca which I've both seeded and bot in flats. Of course if you have a large area to fill you can't go wrong with one of the Wave petunias.

Nice of you to help others with their gardens!

If you need something quick, perhaps Nigella which flowers blue (or white or pink or a mix). The blue would probably look quite nice with the cal.poppies - I'm thinking about this from seed since it's inexpensive that way.

Another option for purchase would be the sun tolerant impatiens - one with the orange/apricot flower might look nice, but with the saparonia a pink might even be better. I think the dark foliage would be nice with this mix.

I also love gomphrena and I love them with california poppies. There are the slightly taller airy ones from seed and the dwarf types you purchase.

Ive been gardening for about ten years now.. it took me 6 years to grow anything besides perrenials and shrubs, and even though my first loves will always be roses and daylilies, I appereciate annuals now in a whole new way.. I added 5-6 different types every year to see what I like and what grows easy from seed every year..

Mixed Annual and Perrenial bed...

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12-18 inches Calendula, you can get some pretty mixes, it blooms and blooms till frost and beyond.. a very hardy annual...

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Snaps up to two feet depending on variety, great color combos, very hardy as well...

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Cosmos, doesnt matter what kind to me this is "picotee" I like the sensation or all white mix as well..

you can also grow the sulfer mix yellow and orange, much shorter 2-3 feet

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Hibiscus Manihoot, yellow annual.. lovely, you can kinda see yvonnes salvia in the background on this one...

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Triple yellow Datura

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Single White Datura.. this one is the BOMB lovely frangrance and just wonderful plant..

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Ive grown several types.. you cant grow wrong with daturas..

Plains corespsis, wonderful medium hieght to add to border 2-3 feet, plant in front of cosmos,

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Nicotinia Sensation Mix 3 feet or so here, lovely frangrance.. long season bloom power.. quick grower.

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Annual Phlox.. growing even more this year.. last year this spread quite a bit..

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Annual Poppies, im adding several more types this year, including some of the peony types.. wonderful hardy annual, early season interest, and long blooming times. Great for our zone or colder.. the warmer you get the harder it is to great flushes of color...

Laurens Grape Poppy

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California Poppy

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I also grow petunias every year.. Morning Glories, Four Oclocks,

I grow all of my annuals from seed, saves a ton money on that way..

Silverkelt

I love the idea of verbena bonariensis - but I just planted all my verbena in my regular bed and have no more for the strip. I was given erroneous information on germinating verbena and so for years it was such a struggle for me to get any seeds to germinate. Finally this year I confronted the seed seller and discovered there was an error in the instructions. I managed to germinate a few plants which I have then planted out into my yard - only this year. Who knew these seedlings resembled poppy seedlings.

I did think of nigella GGG - but I couldn't find seeds at LOWES. I'll have to search around to see where else to get these seeds. Like the idea.

Silerkelt - nice garden photos. many of your suggestions would be a bit too tall for the strip. the plants I need should be low so as not to cause any blind spots.

Ianna

Easy low-growing plants from seed are nasturtium, forget-me-not, and annual flax (red flowers) planted thickly.

I didn't think of flax nor nasturtiums - but that's a great idea. They do fill up a space fast.

I vote for gomphrena. It will bloom until frost and is as carefree a plant as you can find. It makes wonderful dried bouquets too!

I'll add gomphrena too. I've not dabbled as much in annuals as I have with perennials so normally I sprinkle wildflower seeds to fill in spaces. But this time around I'm concencentrating on keeping things neat.

Friend of mine uses strawberry plants in that type of border so both can share. It is used as a ground cover.