Paper Bowser World and Paper Bowser World: Operation G.R.O.M.
Remember that bit in Paper Mario And The Thousand Year Door when you got to play as Bowser for the first time in that brilliant parody of Super Mario Bros? Remember how you cackled with laughter like a raving Victorian asylum inmate and wished there was a whole game based around that idea? You weren't alone, and now there is.
We fell in love with PBW and its sequel instantly. They look and sound great, play amazingly well for fan games (G.R.O.M. in particular has some level design that wouldn't be out of place in an official Nintendo title) and do a fantastic emulation of the their inspiration, right down to the scene transitions and authentic Paper Mario sense of humour. We like. We like a lot. More please, Toodles Team.
Get both of them at Mario Fan Game Galaxy.