I am not sure what you mean by "Punchy" colors - you like it bright?
I like Phlox Robert Poore, it's a long blooming late season eyecatcher mixed with purple ruellia. Sprinkle in some orange cosmos and bam! There's an eyecatcher all right :)

I am endlessly confused about how to combine things effectively. I have a lot of great plants, but don't think I have many really great combos, so I'll be watching this thread to look for ideas!

Here are some plants I have in sun that (i think) have a "wow" factor:

Small trees-
Vitex Agnus Castus (blue flowers)
Amelanchier (for fall color)
Grancy Greybeard
Japanese Maple
Cotinus "Grace" (lovely big purple leaves)

Shrubs-
Loropetalum (especially if your door is purple!)
Spirea "Neon Flash" (it really is neon)
Callicarpa americana (incredibly purple berries, starting in Aug)
Fothergilla "Mount Airy" (bottlebrush white flowers)
Weigela "Ruby Queen"

Perennials-
Echinaceas
Rudbeckias
Agastache (i have purplish "Tutti Frutti" and an orangey "Coronado")
Monarda "Cambridge Scarlet"

I have noticed that both yellow-orange Rudbeckias and pinkish Echinaceas look super against purple Loropetalums. That's about all i have for good combos!

The photos on the Cottage Garden forum give some great ideas for combinations.