Coins aren't as easy to make "pretty" as paper money is--there just isn't as much room! And today in the US, we have to have Liberty, In God We Trust, and United States of America on each coin. Also, the denominations of all of our coins are spelled out in words--the coin says "quarter dollar", not "25 cents". By the time you get through all that essay writing, there isn't much room left! Some of our 50 State Quarters (and the 6 territory quarters) looked nice, but the side with Washington was just crowded with verbiage! I do like our newest cent, though, with the shield on the reverse. On the other hand, can you even tell me what's on the back of a dime? And if you look, still I ask if you can tell me what's on the back of a dime!
Countries with monarchs--and even the Commonwealth, many of whose members still put the British monarch on their coins--essentially limit themselves to one side of a coin, since the monarch takes up the other side. Still, there are many beautiful and interesting coins in the world, and you'd be surprised at what's displayed on them.
So with that introduction, here's our first "cool coin":