I like the standard colourwheel complimentary colours together, like purple and yellow or blue and orange, etc. red and white is striking too.

I was looking forward to other people's creative comments here. I don't give too much thought to color combos. I just plunk things where the conditions are right for them and pray.
I did happen to put a Limelight hydrangea next to a Chocolate Joe Pye Weed with a barberry in front. That looked interesting all summer. Even before anything bloomed. I felt quite accidentally artistic.

Melampodium, 'New Look' celosia and Agastache foeniculum make a nice reseeding threesome for me. I throw in 'Purple Wave' petunia in front on occation as well.

tj

For the Hummingbirds, butterflies, any of the Agastache are big draws. I have them in a feathery red, on the dry gravel bed. Small, 12" Hot Poker I think is the name. I also bought blues on recommendations from folk on Perennials. Then I found some dark pink ones as annuals, at the nursery this spring. They came blooming, were in flower all summer till snow fell. Got about 24-30 inches tall. Wonderful flowering all season, huge draw for the Hummers and all kinds bugs.

A butterfly bush will help draw Hummers and butterflies, though the bush may get large. My mother has one beside her deck, has the hummers visiting all summer. Does need some spring trmming each year. They come in purple, light and dark, white, pink, yellow, to blend with any color scheme. Silver leaves set off darker green plants well.

I am not the best at combinations, just pick colors I like best, toss them all out together. I don't get much time from my Rudibeckias or Heleniums, would not make them a focal point in my garden. Daisies, do give me nice bloom times, especially if you get different varieties. My singles bloom, then the double raggedy ones take over.

You might consider sticking Lily bulbs in, they can come in all colors, bloom over most of the summer. I have the Asian, Trumpet and Orientals, which each bloom at different times. Gives you a great show, wonderful smells wafting around even for older folks noses!

Something my mother enjoys, gets compliments on are her Tree Peonies. She has just a couple, but they bloom extravagently! They get about 3ft tall, and are covered with blooms in early spring. It took a couple years to get going, having more than 1-2 flowers, but it is happy now! Tree Poeonies flower with plate sized blooms, come in colors that regular Peonies don't have, like yellow,purple and striped. My mom has yellow, semi-doubles, gets about 30 on her bush. People even stop on the road to ask about it! She lives in town, so bush is very visible. They are a really tough plant once established, take cold and heat, nice green color the rest of summer. Plain bare sticks in winter.

You might check out the newer small Daylilies, quite a variety of colors and shapes now available. Stella can be nice, but so are many of the bright reds, new yellows, which rebloom even better.

I won't even go into bearded Iris, so many colors! All are fabulous choices. I love my tiny Siberian Iris, only bloom a few days, but wonderful, among the earliest bloomers. Also the dwarf Iris are among my favorites, have several colors, just so cute.

Try to layer things a bit, so new, later blooming plants mask the first bloomers dying away. I like the smaller bushes to add structure, so plant growth and bloom come and go around them. My bushes mostly bloom very early or later towards fall. A pretty trellis or item of interest, fountain, are nice to build around. Bird sprayers are getting popular, keep the bird bath filled with clean water to drink or wash in. Birds need reliable water, not always puddles around.

Stepping stones from pieces of slate, have been very helpful to me for places to walk between the plants for trimming or weeding. Can help give you edging for plant groups in a bed. Keeps me from crushing the dirt down firm, solid place for my feet, saves time going around the beds to come back to the other side, trimming is done in a timely manner.

Thanks for the responses. Mom is now moving!!! This means hundreds of bulbs dozens of perennial species and a handful of trees and shrubs need to be dug and moved this spring. New house has forsythia and rose of sharon galore. Main design consideration now: plantings around rose of sharon.
Thanks,
Tyler.