There are lots of Koopas in the Mario world and I wish I could show them all, but there are just too many so I'm going to identify 3 uncommon ones for.
Boom Boom is a boss Koopa that is pretty new and has not been seen since Mario Bros 3. You may have seen him in Mario Bros U, Super Mario 3d Land or Super Mario 3d World. Each time you fight Boom Boom in a game, he gets stronger. For an example, in world 6 of Mario Bros U Boom Boom has wings.
Clonkdors are super new and are only in the most resent game, Super Mario 3d World witch came out Nov 22 2013. You may not consider them a Koopa but look closer to find out why I do.
The football Koopas are also super new and are also only in Super Mario 3d World but you may have seen this Koopa with out of his football suit in world 5 and 6 of Super Mario bros U.