I am biased since I really enjoy my 4 o'clocks, but they could go well with bamboo. The 2 foot tall shrub-like form and beautiful fuschia color will contrast the slender upright form of the bamboo. 4 o'clocks grow fast in Ohio, and produce lots of seeds in the fall. My first generation was not fragrant, but now my second smells like 'wild orchid' candles that you can find at retailers.

For ground cover, I like Portulaca grandiflora (moss rose). Here in Columbus, they come back every year. Seeds are best left to fall directly on the top of the soil in the fall, so they can reseed. Several varieties are available in every color you can imagine. They seem to do best in half sun half shade. Good luck!

Thanks to Brian K for the suggestions! Anymore?

I read that clover puts nitrogen in the soil, so I am allowing that to grow around my bamboo as a ground cover.

One thing I keep in mind about bamboo companions it that bamboo is shallow-rooted, so a deep-rooting plant like roses or some shrubs would probably not compete with it much.

Thanks Bruce, Clover is a good idea both for ferting and for aesthetics. I am really thinking on the bigger visual scale. So far I think am going to plant a dwarf Japanese Maple, a rhodo, a tree peony, hostas, and a few clumps of big grass in the sunnier spots.

Ornamenal grasses and bamboos go very well. Just did a bunch of inground planters of both, and very happy with look, even though the grasses are small.