You know, my very favorite is good old blanketflower, Gaillardia aristata and its hybrids, especially if you DON'T get the dwarf types since the long stem ones are better for cutting. The plants live for several years, though not forever (mine last about three or four years, but do self-sow).

Angelita daisies are pretty good too (Hymenoxys acaulis), and chocolate flower (Berlandiera) and even brittlebush flowers aren't bad. I'm always cramming bougainvillea blooms into vases here and there too.

Hopefully some other folks will chime in with a more diverse palette of colors. :) Let us know what results you get from whatever you try.

Take care,
Grant