I've had various Echinodorus flower, along with floating Frogbit, and those other plants mentioned like Anubias, Aponogeton.
Except for the ferns and mosses, all of our aquarium plants do flower, in their natural state, but as someone mentioned they may rarely do so in the aquarium. Some require emersed cultivation, others need brighter light (which means CO2 diffusion and higher nutrient supplementation).
Byron.