If you are looking for a cactus with brilliant flowers then Trichocereus grandiflorus is probably it. Native to Argentina this is a spring to summer flowering succulent with many hybrids now available.
Over time it can grow stems to around 15 to 20 inches, however it is a little slow to achieve these lofty heights.
The original species were mainly a clear red, however with variations soon found hybridisers now have pink and yellow varieties as well.
The flowers are large with 3 inches not being unusual.