Would be Frikart aster except I've had problems with them not overwintering. The new Geranium wallichianum hybrids are also good; would be G. wallichianum 'Buxton's Variety' except plants sold here are only blue during cool weather, mostly at end of season.
Gaura lindheimeri 'Siskiyou Pink'. It started blooming in late May and last year it bloomed all the way to frost. It is also quite drought resistant. Joe
An apricot coloured alstroemeria obtained from another gardener, so no variety name. The plant starts flowering in June and will bloom its guts out till frost. This variety sets no seeds, which I'm sure helps it to be covered in flowers rather than tapering off as the seed crop gets heavy.
Centranthus ruber....spreads like crazy, but don't we all? Pretty glaucous foliage, and seems to bloom forever.
I'm sorry that I do not know the botanical name for any plants but my favorite long blooming perennial is the purple coneflower. This was my first year to have them, and has become my favorite.
For long blooming, Salvia transylvanica performs all season long, from the first spikes of blue flowers in late spring right up to first frost.
Phygelius, the Cape Fuchsia. I'm looking forward to buying one of the new salmon colored ones next year. Mine usually blooms June through November and is evergreen in mild years. Hummingbirds like it and slugs don't eat it. A white flowered Gaura is a close second but sometimes it is short lived for me.