I often thought that some shade loving plant that fixes nitrogen would make a good companion plant for bamboo.

Hosta is sometimes planted with bamboo.

I may have read this wrong, but if the container is open on the bottom it's not going to contain anything.

Second hostas if in shade.

Delicate ferns look good too.

Thanks so much for the input guys.
I may have neglected to mention that this area will be in full sun during the hottest part of the day. Hosta's and ferns I would imagine to be stunning beneath bamboo, but I'm afraid that in my situation they might roast in the summer. one small section will have some shade and I think that I might try a hosta or two there.
Also just got the bamboo--Phyllostachys bambusoides -"Castillon" While I've read that this can get to 35 ft. apparently here in So.Cal. 20 ft is more likely and probably slightly less in my planter.