Purple potatoes

I am looking for those types of potatoes that have a rich purple colored flesh on the inside. Does anyone have a good variety to recommend, and where to get them? I have been growing some purple potatoes that i got from wal-mart a while back--i dont even remember the name of them, which usually are all purple throughout, but this year they seem to be reverting to just purple skin, and the flesh growing in nearly solid white.

Thanks!

Here's a list of purple varieties:
http://potatoes.wsu.edu/varieties/blue-purp-vars.htm

Thanks, i am thinking that Congo is an enticing sounding type of potato to try!

Check The Potato Garden's catalog and see what they have. I've ordered from them previously and have had good service. They have several purple varieties. (Click the link for the pdf catalog.)

http://www.potatogarden.com/index.html

I've ordered from them, too. Good taters and very pleasant to deal with.