They will need staking. There are many good waterlily dahlias and some that should do well are Pam Howden, Taratahi Ruby, Wildwood Marie, Cameo.
These can be viewed from various commercial growers catalogs located at Dahlias.net Big List.

Here is a link that might be useful: Colorado Dahlia Society

I second the vote for every one Huey named- all top quality and beautiful colors. They are all tall and will need staking. Pam Howden is/are among the tallest in my garden again this year- 5+ feet last year and heading that way soon in 07. Cameo is more 3.5-4 ft. Taratahi Ruby is one of the most vibrant dahlias I've ever grown. Get them all!

Thank you for your recommendation. What would you use for staking in containers and what's the minimum diameter for the container? Thanks again!