Zinnias come to mind. Or tithonia, bachelor's button, some vines for height?

Tracy

Got any particular colors in mind?

-Dwarf Spray Sunflowers- more branching with more blooms than your typical SF- Yellow
-Marigolds come in a wide variety of sizes & colors. Some nice ones that are taller with big, poofy blooms in yellow, oranges & red-mixes
-Tidal Wave Petunias can be trained into a hedge-like form unlike their plainer relatives, and come in pinks, whites, purples and variations of same
-Annual Mallow- I'm trying "Vulcan" this year which is a deep reddish/rose. Also have Musk Mallow Pirouette (white) in the mix.
-Daisies! Shasta (although perennial) comes in several forms such as your typical wild form, a clumping form, and 'crazy' which has more cactus-like blooms. Argyranthemum in the Proven Winners brand is a lovely yellow ("Butterfly") or creamy yellow ("Vanilla Butterfly") and is about 18" tall- again is a daisy-like flower. Painted Daisy: I've got packets that say annual and perennial, so not sure what to expect from these. Multi-colored daisies.
-Larkspur is the annual form of delphinium if you like the spiky varieties, but might be too tall for what you want. Not sure how tall the "Gentian Blue" gets, but that's a lovely open-lacey form rather than the spikes.
-Bells of Ireland- again, a spikey thing in green. Not sure if you can find it in a nursery, though.
-Rudbeckia comes in a couple of annual varieties: Toto and Prarie Sun (or Irish Eyes...one of those is the annual one). I think "Becky" might be annual, too.
-Foliage only: Coleus comes in a variety of colors & sizes to liven up your areas.
-Herbs: Basil comes in a nice purple foliage. Sage comes in a tri-colored form (purple/whitish/greens)
-Four O'Clocks- many colors
-Balsam Impatiens are 'bushier' and taller than their shorter counterparts- Pinks

I put in a lot of white 'Rocket' snapdragons close to my three groups of purple cone flowers.
I also have white and pink Lavatera and a pale yellow/buffy colored marigold called 'moonlight'.

i really like orange flowers with purple cone flowers.

i know you said something other than cosmos, but do you have the cosmic series? they are shorter and have smaller double flowers. also looks great with the russian sage.

you could try the star zinnias as well for the same effect.

Thanks all for the suggestions. The cosmic series Cosmos sound nice... I don't have those and I adore cosmos. I'll do an internet search and see what they look like.

White rocket snapdragons, salvia farinacea "victoria blue", angelonia (white, pink, purple or lavender) all have that spiky "perennial" look that will work well for you. Be sure to pinch new plants for bushy growth.

My long time favorite is agastache Blue Horizon and I always save some spaces for it. It gets over 2 feet tall and flowers up to a hard frost. Fills in any bare spaces among the perennials and is showy all summer.

How about cleome? Comes in white, pink, and purple. This is a large annual and can get nearly four feet tall and several feet wide. I love it!

Here is a pic from last year of my cleome behind some zinnias. I'm not crazy about it with the orange, this year I am growing it with pastels, purple and white.

I second the cosmic cosmos series as being fantastic -- some of my absolute favorite annuals all time, but they really only get about a foot high for me. I almost always use them as edging plants. In terms of two feet, I agree with the balsam impatients, which get at least 18 inches for me, with pretty double flowers all up and down their stems.

Emily

Border dahlias! Absolutely stunning plants. They grow about 2' tall and bloom continuously until frost here in zone 6. You can buy them at very inexpensive prices at the box stores in flats. So cheap you can treat them as annuals if you want. They might even come back next year if they are heavily mulched over the winter.

Lyn

Do Dahlias like sun or shade - I have morning sun until around 1 and then mostly shade - I too need some fill ins in a brand new perennial bed that is still in the making. Do you suggest grouping them in 3s? for a nice look?

Fern

Coreopsis tinctoria would look nice.

Fern .... I have border Dahlias in full sun and part sun and both do well for me. Grouping in threes would look very nice, however, I tend to just plop them in the ground where ever I see a bare spot because I like them so much.

Lyn

I have 5 varieties of Celosia/Cockscomb amongst the perennial border to fill in and am looking for even more varieties. Sounds like a good thread, I'll start one now.