Build a cube that can easily run 5 colors, each color pair, as well as tri-colors if you're smart about it. Meant for maximum replayability. Themes:
White (knights)
Blue (illusions)
Black (benefit for a cost)
Red (value from attack)
Green (auras)

Azorius (control)
Boros (equipment)
Dimir (control)
Golgari (graveyard)
Gruul (midrange)
Izzet (spellslinger)
Orzhov (lifegain)
Rakdos (aggro)
Selesnya (enchantress)
Simic (evolve)