Anemone sylvestris and/or Centaura montana, Geranium 'Rozanne', Echinacea 'White Swan' or 'Fragrant Angel', Anemone hupehensis.

Please post pics, I've gotta see this yard with four beds!

I wouln't limit yourself to just perennials and I'd make each bed do double duty re time of interest.

My seed grown Angel roses fit the bill and give a long season of interest. They start blooming in late May/early June, have their biggest flush of bloom in June/early July but then continue to bloom into fall. In fall they are covered with small bright red hips that the birds love. I've never seen them in a garden center so you have to grow them from seed. In a few years you will have a dense, showy hedge of them.
In June:
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In Oct./Nov.:
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A mass of smaller hardy hibiscus are great and, since they are VERY slow to wake up in spring, you can plant lots of spring bulbs with them for a spring show and then have a late summer show from the hibiscus.
In spring:
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In August:
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Peonies are great to mass with tulips too. Angelique tulips look like peony flowers and bloom about the same time as the peony foliage is developing, so it looks like the peonies are blooming early. Then the peonies hide the dying foliage. Queen of the Night tulips make a wonderful third companion. If you have a long, not too wide, bed of peonies, the staking of them is easier because you could just make an ornamental 'fence' (use black plastic chain strung between short posts painted black?) around the whole bed at the height needed to keep the peonies from flopping over.

A bed of fall asters or mums would be another one that could be a spring bed first.

I like the Anemone sylvestris and Echinacea 'White Swan' suggestions. I feel like Rozanne and Jolly Bee can be "inconsistent" otherwise one of them would be a lock.

Can you tell me more about the Angel Roses and hardy hibiscus (spring bulb mix is a great idea)? Mainly cultivars and latin names.

These beds are actually quite small and by massing I mean 5-10 plants. Each bed will have a tree and a few shrubs to fill in the season of interest.

1 Bed has Betula nigra 'Heritage' as the anchor
1 Bed has Carpinus caroliniana as the anchor
1 Bed has Ginkgo biloba 'Autumn Gold' as the anchor
1 Bed has Tilia tomentosa 'Sterling' as the anchor

Maybe I'll post pics before hand to drive some better ideas...I'm terrible when it comes to perrenials.

My goal is to have a casual formal look in the front yard, keeping it farily simple per bed since there are 4 of them in the front/side yards.

Two perrenials that come to mind with nice foliage and color that meet your requirements are peonies and gas plant.

Is there a superior dwarf peony cultivar with strong stems?

I've never seen a unstaked peony not flop.

My choices would be these four:

-- groupings of daffodils with hostas or daylily's interplanted (to hide the dying foliage later on) for early spring;

-- netpeta or liatris for early summer -- I love their spikes and foliage and lavender colors, and either would be beautiful as a single planting;

-- echinacea for summer -- plant two or three varieties of different heights and pink colors, say Kim's Knee High, which grows to only 24" (medium pink) with Ruby Star (darker pink), which grows to 28", and/or Hope (light pink), which grows to 30";

-- asters for fall -- I like cordifolia Wood's Purple for the front (short and a beautiful lavender/purple), along with Bonningdale novi-Belgii (24"-30"), which is a white double, in the middle or at the back.

Now you've got me thinking and I just may steal your idea of four single-plant beds!

Let us know what you decide.

For the angel roses, the easiest thing is to give you the link to where I got my original seeds. Botanically, they are the species miniature China Roses.

My pink hibiscuses appear to be similar to the ones on this page - I know they were Disco Belles (I now grow them from seeds I harvest from the existing plants):
http://www.paghat.com/rosemallow-discopink.html

You're changing the game with trees in the beds - you are looking for shade combination...?

The best non-staking peonies are single ones - or tree peonies. My suggestion was - if the bed is narrow enough to be a row of peonies, then instead of using individual peony rings the support them, corral the whole bed with an ornamental 'lasso' (the chain) and let them support themselves by leaning over the chain.

Here is a link that might be useful: angel rose seeds