Which flowers that are perennial that grows in 5 gallon pot

Hi,
I mostly have all hibiscus and roses in my garden. I have about 5 (5 gallon) pots left in which I want to put some flowers. I would like to put different flowers in these pots for this year. i know there are tons of flowers and liking of the flowers is in the eye of the beholder. I just want to know which flowers will grow fine in 5 gallon pot (and i dont plan to change them to a different pot) and also it will flower every year.

Thanks,
Sunray

Most of the plants generally thought of as perennials will work in a 5 gallon container.
These are herbacious (non woody) plants that can live for more than 2 years. Some go dormant and lose all their top growth, some hold onto some green through the winter. Some even bloom in the winter. Milpitas is very mild, so evergreen perennials ought to work just fine. Plants that grow from bulbs, corms and other sorts of tubers are good in containers, too. They usually have a longer dormant period, so might not be so attractive most of the year. Daffodils, for example are in bloom for a month, have leaves for about 4-6 months, then nothing. I would not choose daffodils where I wanted a year-round show.

Are you planting these in sun or shade?
Are these standard 5 gallon nursery containers? Or something else? If they are shallow, wide containers you might grow more than one plant in each, though the plants would be smaller.
Do you want something that hangs over the side, a trailing plant?
Do you want something more like a vine, that climbs? There are not a lot of vines that can stay in a 5 gallon can.

I dont plan to move these pots so there will be sun outside most of the day outside.
Yes, they are standard 5 gallon nursery containers.
They are not wide containers and I think I would like to have 1 plant per pot.
I dont prefer anything hanging or a vine.
i think I would like something like Dahlia but last winter they did not survive. I did not protect Rose and Hibiscus either but they survived but the Dahlia completely went dead (atleast did not have any leaves and stems were all dry by the time winter ended)

Dahlia dies down to a tuber sort of root. They are usually lifted out of the soil and stored, but I do not know the details.

OK...
Perennials or small shrubs.
Full sun, or close to it.
Zone 9b to 10a. Since containers (especially black) can get warmer in the summer, but colder in the winter, lets look into 9b (colder winter).
Upright.
Size appropriate to keep in a 5 gallon can, so maybe 1' to 3' high. Taller might work, but it would blow over.

Grasses or grass-like options:
Miscanthus sinensis 'Yaku Jima'
Carex barbarae
Rhynchelytrum nerviglume
Phormium tenax and hybrids, look into the smaller varieties.
Hemerocallis hybrids- look for the evergreen (or nearly evergreen) types.

Basal mass of leaves, tall flower spikes
Anigozanthos- look into the sizes- there are larger and smaller types.
Geum chiloense

Rounded mounds, flowers only a little above the leaf mass
Dianthus plumarius and similar- some are fragrant
Iberis sempervirens (not hot reflected heat, best with a little protection from afternoon sun)
Salvia officinalis, in any of several leaf forms or colors. This is the sage used in the kitchen. The colored leaf forms may be more interesting for show, but you can also cool with them.
Purple Sage, Golden Sage, Tricolor Sage, or Bergarten, a larger leaf form.
Salvia nemerosa, S. x sylvestris, or Salvia x superba (confusion in the trades among species, varieties and hybrids- basically all are low masses of leaves with upright flowers, often blue-purple, but there are also white or pink. some are taller)

More shrub-like
Ruellia britoniana (may get too big)
Scabiosa caucasica
Salvia elegans 'Golden Delicious'- this is one of the dwarf forms. If you go shopping and someone tries to sell you the straight species insist on the dwarf only.