purpurea (often called Rudbeckia) is the showiest species.
The Iceland poppy (P. undicaule), is one of the showiest species, having grey-green pinnate leaves and flowers varying in colour from pure white to deep orange-yellow, orange-scarlet, &c. Specially fine varieties with stalks 18-24 in.
Senecio Doronicum - One of the showiest and most useful of the group, 1 foot to 3 feet high, with stout stalks of large bright yellow flowers in early summer.
Salicaria is the most familiar plant of this genus, and one of the showiest.
S. Speculum, with numerous open bell-like bright violet-purple flowers, is one of the showiest of our annuals.