[wittzo]

The Flower and Spyke standard size card sleeves are a good start.

You could have class specific sleeves with a simple action scene or some sort of art on the sleeves and have matching deck boxes. Gameplus could make them, since they're already the ones making the existing sleeves for SJG. You could use the art from the X class cards.

Southern Hobbies has their exclusive Munchkin CCG playmat.