cornflowers and larkspur last for ages in water. also, i grow cosmos, nasturtiums, canterbury bells,campanula persicifolia, icelandic poppies, scabious, geums, lupins, cleomes, lavatera trimestris, hollyhocks, calendulas, rudbeckias, incarvillea 'cheron' (not ther nasty pink ones but delicate pale primrose, very easy,) - all these are really easy, growing in one season from seed and mostly lasting well. for fragrance, go for pinks, sweetpeas, sweet william, wallflowers. i plant many flowers at the edges of veg beds, or around paths or climbing with beans (morning glories, cobaens, climbing nasturtium, black-eyed susans (thunbergias) go for it - flowers are too lovely to ignore.
also, bulbs such as the nanus gladioli, lilies, freesia, shizostylus and many more.
i grow all hardy annuals in September and either leave them to it or shelter in a coldframe. - they flower early and well next year.
good luck, i have flowers in the house nearly all year round.
cheers, suzy