I've put some New Guinea Impatiens in a container. They bloom nicely, don't need much sun and grow about 5-6" tall. Alternatively, an autumn fern might work, but of course it doesn't bloom, but the fronds change color.

katydid....i am wondering just how tall are you wanting and any specific colors?

How about a tall coleus? I just bought "Giant Exhibition Coleus" and am really looking forward to seeing how big they will get! Most coleus prefer at least some shade. They are grown for the leaves rather than flowers but when the leaves COME in the colors of many flowers, why not? I liked them last year (bought shorter, "Red Dragon" variety) because unlike flowers, which have to have blooms to have color, the coleus are colorfull all the time. I planted shorter blooming things around them in the pots: snapdragons and lobelia.

I'm looking for something as tall as a spike. It doesn't really matter what colour it is.