delphiniums too...and many more. I think it is Tracy DiSabato Aust who wrote in her books about this. Check her out here or in your library.
http://www.tracylive.com/

The rebloom that I know from experience that is very good is Achillea (I have 'Strawberry Seduction'). In fact I like the 2nd flush better than the first as it lasts well into October and the stalks are better able to support the blooms if one has pinched back enough (to encourage the re-flower).

Some daylilies, The everblooming oves. I cut down my musk mallow when it gets lots of seeds to about 6 inches and it reblooms. It also cuts down on a multitude of new plants the next spring. There's just enough to replant if needs be

Tracy DiSabato Aust's book is great for this! I normally just get everything at the library. This one, I had to buy! Great practical tips, not just eye candy. My phlox and asters have not flopped since I started pruning them following her instructions. Knowing what to deadhead, and what to leave: comprehensive.

Here's a great link.

Here is a link that might be useful: Off with their Heads

Asclepias tuberosa has bloomed 4 times or more per year when cut back bedore seeds set.

And here is that second flush from this single plant "Strawberry Seduction" Yarrow. These blooms should last into October.

Many perennials.

The red valerian mentioned is an example, though I also tend to keep up with cutting off it's spent blooms to avoid too much reseeding.

Currently we have a lot of colour in the garden from the garden phlox which were deadheaded.

I've never understood leaving dead flowers on plants at all unless you're trying to get seeds. The last thing I want to look at is dead flowers. They come off several times per week at least. This keeps things blooming more constantly than in spurts, and avoids shearing, which can make plants look like chia heads. For plants with the ability to do so, if you cut individual flowers off when they start forming a forming seed pod, a new (individual or stalk of) flower will start to emerge long before it would have if one waited until the whole stalk or 'flush' was finished.