Persicaria amplexicaulis 'Firetail' or 'Taurus'

I don't know if this is true for everyone, but my fernleaf bleeding heart starts blooming in about early may, and will keep blooming until about september

Dandilions.

lol chelone
My longest blooming perennial is scabiosa "butterfly blue", but I know a lot of people on this forum have dissed it because they say it's sloppy and not 'neat'. Well, yeah, but it looks like it was designed by Dr. Seuss, I love the color, and it blooms it's head off from now till fall (and I mean, is still blooming when my black eyed susans are done!) To it's detractors, ok, it isn't a tidy little golf ball plant, and it does need deadheading, but what doesn't? The only bummer I've found about it is that it is short lived, but even knowing that, I've put in 8 more this year alone. It's worth it to me, even if it will only live a few years! Nonstop bloom from now to frost? Oh, yeah!
Lexi

I am going to get thrown off this forum for being so BORING, but I will repeat my favorites:
Centranthus Ruber (red valerian) (early May to frost)
Salvia nemarosa Caradonna (late May to frost) (and looks nice with Rozanne...)

Gaillardia blanket flower 'Goblin.' Just blooms like crazy from June thru October....if you deadhead!

Johnson Blue Geraniums

Stella D'Oro daylilies bloom from about now until frost. I prefer the yellow Happy Returns daylily which blooms for a long period but now quite as long as the Stella D'Oro.

Gaura is one of my favorites. It blooms from July through Frost. It tends to be short-lived but leaves a few seedlings behind each year.

Count me in as a fan of the gallardia, for long blooming perennial. Stella D'oro daylilly does not repeat that much I am a bit dissappointed with it, and I have quite a few of them. They are lovely when in bloom , jsut don't last that long.Scabiosa and Knautia are also long lasting.

Coreopsis 'Moonbeam'
Campanula 'Blue Chips' or 'White Chips'
Echinacea purpurea - non-hybridized

Put these three together in a sunny spot and you'll have a constant sweep of mixed color from early-June through November.

Martie

Can't forget hybrid (aka oriental) Hellebores - they start in March and their flowers are just now gone, as of mid-June. If I look closely I'll probably spot some more that are hanging on. OK, ok, technically, they bloom once, but the flowers persist and look good for an unbelievably long time, at least in certain conditions.

And, I second mayalena's vote for red valerian (centranthus). I'd grow it even if it bloomed briefly, because I love the peachy-red color, but it keeps on going.

Balloon flower, if deadheaaded, will bloom from now until frost. Can't beat it with a stick, as they say. I'm not wild about the somewhat stiff, upright form, but the color is fantastic.

Delosperma - IF you can get it to overwinter! Blooms from May to November here.

I planted this three times, lost it three times, and gave up. The next year I found two tiny plants that must have reseeded, and they are back for the second year now! Hoping it will spread and stick around for a few more years.

:)
Dee

I've given up on delosperma too, it's never come back for me.

And I have a slight correction to my post about hellebores. Some of them still have perfectly good flowers on them. I guess "perfectly good" is faint praise, but really they do bloom practically forever in some situations.