Kind of a difficult question because there are literally thousands upon thousands of possibilities. Hard to narrow it down without knowing what kinds of plants you are interested in, what your garden space is like, style, and so forth.

I am not in your zone but since no one is replying I will give it a whirl.
lobularia
tagetes
cosmos
Impatiens balsamina
viola, the pansy type
zinnia
columbine
calendula officinalis
portulaca
mirabilis jalapa
alcea
Ipomoea
I have grown them all from seed directly in the ground

This post was edited by emmarene on Mon, Oct 21, 13 at 17:54

thanks - that's really helpful. I will give those seeds a try. I also want to just see what will grow in the ground.

I have only grown a few bedding-type flowering perennials successfully from seed: rudbeckia, sea holly, columbine, blue flax, and achillea ptarmica. I have also managed to get foxgloves to grow, but I think they are a biennial. It's easy to grow members of the iris family from seed- especially fortnight lilies and candy lilies.

Zinnias, ipomoea, portulaca, calendula, violas, cosmos, and tagetes grow from seed here, but they are all annual. I have had some vincas survive for more than one year, though.

Annual flowers are super easy to grow from seed. I grow California poppies, breadseed and shirley poppies, peony poppies, Iceland poppies, larkspur, red flax, paludosum daisies, bachelor buttons, nigella, bells of ireland, toadflax, Queen Anne's Lace, and lobelia. I have trouble getting vincas and pansies to grow from seed.

My list was all annuals; my mistake. My best success with perennials would have to be Iberis. I have them as a very low hedge. I would not have been able to buy so many plants from the nursery due to cost. The hedge has at least twenty plants.
I have two Gerbera Daisy seedlings, I am trying not to kill them.

Easy from seed Perennials in the SF bay area:
Yarrow
Aquilegia
Hollyhock
Gaillardia (short lived - self sows)
Nicotiana
Dahlia (try Bishops Children)
Verbascum (some are biennial - all self sow)

also:
Tree mallows (lavatera)
Lemon marigold (Tagates lemonii)
gazanias
borage
Phacelia
Monkeyflower (mimulus)
yerba buena (Satureja)

fall = bulbs, so those are some of the easiest now too. Ginger, iris, garlic, calla, freesia, lilies, ...