Maybe a bit more information is needed.
1) where on your property is this plot?
2) Why limit the space to 3x10?
3) Why no tall plants?
4) Would you consider adding an ornamental tree to this bed?

What you've given us isn't really enough information to go by.
Have you been to your local botanical garden, looked at books or magazines or at the very least a good nursery in your area to see what you like?

Getting continuous bloom from such a small space pretty much means that there will be one plant in bloom at a time. If continuous bloom really is one of the goals, plant annuals. It's perfectly doable for that size bed.

Yes I go along with that as I had the same situation as the years went by I added perrenials, by that time I knew what I wanted there. Tricia

I noticed that you posted this on the Cottage Garden forum too (not that that is taboo or anything). Did you want it in cottage style?

I had a similar bed along the house foundation before I enlarged it. It was a shady bed. The trick when working with so small a space is to use mostly 'foliage plants'. I used a lot of hostas in my bed, which kept the bed interesting.

Do you want this to be a low-maintanance area? Is it a dry area? If so I would suggest planting it with ornamental grasses or making the area a sedum bed. Ornamental grasses do not bloom (unless you count the plumes), but add nice texture and arn't very fussy. Lots of interesting kinds and foliage colors. One of my favorites is Blue Oat Grass (Helictotrichon sempervirens)
Most Sedum bloom only in the fall, but they come in a range of different forms, such as groundcover and upright perennials. The plants are interesting even when not in bloom. There are some that have purple, blue, and golden foliage. Butterflies enjoy them.
Euphorbia, Salvia, and Daylilies (especialy Stella d'Oro') are attractive for almost all of the growing season. Plant tulips and such for early-spring interest.
Hope this helps you some.
CMK

Another good idea would be to plant 'Knock Out' roses. They are common but prolific bloomers. They don't get too large in our zone (at least they don't in my yard). There are several different kinds, single magenta, double magenta, pink, and a "rainbow". You might also try a carpet rose or a bunch of mini roses.
CMK

This plot is in the front of my house. There is a small set of steps leading to the walkway to my house. The plot is directly to the right of the walkway to my front porch. The area is limited to 3x10 because that's all that there is...the bottom of the plot if the public sidewalk, the left is my walkway, the top is my porch and the right it my driveway. That's why there can be no tall plants, because there is nothing to have them up against to keep from falling over...

Gaillardia (also know as Blanket Flower) will stay short and bloom all summer.

One fear can be dispelled - most of the perennials rarely need to be planted "against something" to keep them from falling over. They're sturdy enough to stand on their own.

Your only limitation is space and how many perennials 30 square feet can hold. And the look would be more cohesive by planting 3 each of, say, 5 different plants as opposed to 15 different ones. Or use a small blooming shrub as an anchor to plant groupings around - Spirea Japonica "Alpina" is a dwarf variety with dusty rose colored blooms that can sometimes produce a late season rebloom.

For all season bloom, I second the idea of adding some annuals which pretty well keep going until the first hard frost.

Angela, ask yourself some questions:
What colors do I like?
Do I own a shovel, hoe, rake, gardening pruners and trowel?
How much work am I willing to do to keep this garden looking nice?
How much money can I spend?

I would suggest that you first go to your library and check out a good general book on gardening. You want it to cover subjects like soil preparation, watering, sun exposures, weed/pest control. Give it a good read and you'll know more about gardening than 90 percent of the population. (Knowledge is power!)

THEN, lay your plans for soil prep. If you spend all your money on preparing your garden area, it's money VERY well spent. If that's the case, then definitely plant an annuals garden. Go to a big box store and buy 3 to 5 packages of seeds in colors that you like. Assuming your bed will get at least six hours of sun every day, some good bets would be: Zinnias, Cosmos, Gloriosa Daisies, Sunflowers, Oxeye Daisies, Cleome, and Lobelia (the blue kinds). These flowers come in loads of colors, bloom styles, and sizes. If you do a good job of preparing your soil, you can sprinkle the seeds right onto the ground, press them firmly into the soil, water, and they will grow. You'll have a glorious garden that will knock the socks off your neighbors. All this success will make you pay attention to other peoples' gardens, bringing on lots of gloating, but also causing you to ask "What's that?" Find out, and start a list for next year.

Next year, with some experience under your belt, go back to the library and look for a book that talks about growing perennials in your area. It doesn't matter how old the book is, it will be good basisc information. Referring to your local list and your book, start drawing plans for your (probably enlarged by now, even if you just figure out how to go up) bed. Gardening is tons of FUN. Nobody can do it all or learn it all in one year (or even one lifetime). The journey is the joy. "You can do it. We can help." :)

You know what I'd do? In a space like that, I'd fill it with all one kind of plant of a medium size - say 2' or thereabouts. I'm thinking nepeta, amsonia hubrichtii, rudbeckia or baptisia (OK, that one's 3' tall!) You need a plant with a decent bloom period and reasonably attractive foliage for when it's not in bloom. Amsonia in particular has very nice fall color. Down here, lavender makes a great walkway bed, but in z5, sometimes it dies over the winter. You might be able to get two seasons out of it by putting in some clumps of daffodils and squills whose foliage will just get buried when the perennials return.

Amsonia in bloom:

http://www.horticopia.com/hortpix/html/pc535.htm

Amsonia in the fall:

http://www.perennialreference.com/perennials/amsonia.html

I can't find the really fabulous photo of amsonia lining a university walkway. rats.
Another idea might be to make that space your herb garden - oregano, thyme, sage, different kinds of basil and an ornamental pepper or two.

Here's the photo.

Here is a link that might be useful: amsonia in autumn