From the point of view of getting bloom next year, I think it is better to start some seeds in fall. Some can be direct-sown in fall, some need the chilling to sprout. I started some seeds in November last year, and grew them under lights until things warmed up in May, and they are blooming now.

If you consider what you want out of the wildflowers it helps to pick what to grow. Some are favored by butterflies to raise caterpillars, or for nectar, some are liked by hummingbirds, some have edible or medicinal qualities, some are for flowers, etc. There is a butterfly forum and hummingbird forum on GW that would be useful. There are also considerations of height, how well things fill in and whether they are long-lived, will suppress weeds, etc. Some companies have seed mixes designed for specific areas or uses, they might also tell you the best time to sow. Prairie Moon and Everwilde come to mind.

Unless the shrubs are very tall and shade your mulch/shrub spot, or there are numerous trees shading the area, it may be best to try a meadow type of planting. You may also want to consider how dry or wet the spot tends to be, and what type of soil you have, i.e. sandy, clay, acidic, alkaline, etc.

I've had good success with planting native plants that come in pots in the fall. This can get costly though, depending on how much of the area you would like to plant.

Planting from seed is more economical, but there is a chance that some of the seeds will get eaten/washed away through the fall, winter and spring. I found that winter sowing native seeds outdoors in milk jugs helped with this. The GardenWeb's Winter Sowing forum has a lot of great info on how to winter sow in outdoor containers:

http://forums2.gardenweb.com/forums/wtrsow/

This winter I sowed monarda, mountain mint, rudbeckia, penstemon, columbine and many other native plants in jugs, planted the seedlings in my garden, and they are now happily growing.

There are a couple of books that come to mind that were helpful to me when I was planning native planting areas:

The first one is "Landscaping with Native Plants in the Mid-Atlantic Region" by Elizabeth N. du Pont. It's for sale at the Brandywine River Museum shop:

http://www.brandywinemuseumshop.org/catalog/index.cfm/ItemID/BC4DEF15-4E42-4ECF-A8B1545CEBBFCB2B/display/detail

...or you may be able to find it elsewhere online or in a used bookstore.

The second is a book called "Grow Wild!: Low-Maintenance, Sure-Success, Distinctive Gardening with Native Plants" by Lorraine Johnson. This one covers various areas of the U.S., but has a section on meadows in the Northeastern regions.

If you are in the Chesapeake Bay Watershed area, there is an excellent guide to native plants for that area. You can download it online (the file is pretty big):

http://www.nps.gov/plants/pubs/chesapeake/

Prairie Moon Nursery mentioned by hemnancy above has been a great resource for me for seeds. They do have some woodland species, but most of the seeds and plants are for meadow or prairie areas. Check out their website:

http://www.prairiemoon.com/

Last but not least, you may want to consider what type of wild mammals you have in your area, such as deer, woodchucks, rabbits, etc. that could cause difficulty with growing native wildflowers. We have several groundhogs living in our backyard that will eat all the leaves off most anything in the aster or pea family for instance.

Some of my native plant areas have had to be modified from my original hopes for them due to the groundhogs, but I now have a nice non-fenced garden that is mostly planted with monarda and other native plants in the mint family, which the groundhogs don't seem to like to eat. Anything else such as phlox, echinacea, asters, rudbeckia, etc. goes in our fenced area which is surrounded by a concrete patio. The concrete prevents the groundhogs from tunneling under the fence. The fence itself is made up of narrowly-spaced iron bars which the groundhogs have difficulty climbing. They will climb over a chicken wire or any kind of metal mesh fence quite easily (see link below).

Here is a link that might be useful: What the groundhogs are doing while you're not looking

Please be careful about any seed mix or mat marked "wildflowers." That tern doesn't mean anything in horticulture or botany, and most of the plants included will be nonnative annuals (for fast color).

On a site that size, that's already mulched, I would wait until spring and then plant native perennials plants and grasses. Some will bloom the first year; all will bloom the second.

1. Buy plants or seed that are native and are suited to your particular site conditions. A lot of native plant catalogs will have the basic info like whether the plant likes full sun or wet ground, etc. A local or state native plant society might have a good list for your area and might even sell plants or have a list of good vendors. Some soil and water conservation districts also have plant sales but they will not necessarily sell only native plants. I got some great plants from such a district at very good prices.
2. You could scatter seed across the bed in fall and see what comes up in spring but with the mulch already there and with the normal attrition of scattered seed even on ideal ground you might not get much.
3. You can start seeds in containers or whatever and then transplant. I'm simply no good at that so you will need others' advice about how to do that.
4. You can buy bare root plants or small plugs and put them right in the ground in early fall. Someone did that on a large scale at my church and it worked out great but it was not cheap although buying small bare root plants or plugs is much cheaper than big potted plants.
5. Nearer the end of the summer a lot of nurseries and supermarkets sell off their remaining flowers very cheaply. Those plants will be very root bound but they will be cheap and the perrenials will probably survive.
6. Bee balms will spread on their own. If you like bee balm a lot, put some in and eventually you will have many more. Bee balm can be a bit aggressive. I did that in one area that needed some cover and it worked.

Good luck. It should turn out to be a nice flower bed once it's established. With many native plants the first year or two can show very little drama above ground but don't let that discourage you as they are establishing strong roots that are eventually followed by very healthy and very attractive flowers. The planting at my church didn't look like much for about 18 months or two years but now is gorgeous. Some native flowers like to mix with some native grasses but it's not necessary to have the grasses if you don't want them.