50p

I like these heptagonal coins. Much more interesting than our rounds ones here in the U. S., although I think I understand how rounds coins can be cheaper to produce and maybe more practical.

The Royal Mint provides the following rationale, though, for the 50p: 

"The new coin would be the largest denomination in circulation. As such, it required a design that would enable people to easily tell it apart from other coins in their change. However, anything too bulky would weigh down pockets and purses so any prospective design had to be practical as well as distinctive."