Yep, the BRITISH 50p coin is a heptagon so you can't confuse it with anything, apart from the 20p which is also a heptagon! (albeit a lot smaller.)
As it happens, I was watching CSI Vegas tonight and I swear I saw a one-arm bandit (slot machine?) paying out 2p coins. They were copper colour and it looked like the Prince of Wales emblem on them.
http://en.wikipedia.org/wiki/United_States_dollar_coin
I first saw these when I went to vegas, never seen them anywhere else.