Coming in at #4 is Gambit. He's one of my favorite X-Men mainly because he was in the 90s cartoon show. He's also pretty awesome in the recent Wolverine and the X-Men cartoon, though he is still in his theiving days in that show. I prefer him to be on the team, but his dark past is part of what makes him interesting.
"Smooth and suave, Gambit always seems to have the winning cards - especially when this ragin' Cajun charges up the deck with his mutant power, dealing defeat to villains."
I'm kind of surprised such a love-him-or-hate-him character would be the fourth card in the series (still no Wolverine?) but I love him, so I won't complain.