My brother and I have been playing Mage Wars by email. It requires that we trust each other on card planning (though we could both make blind emails to a third email address and verify after if that were an issue) and dice rolling (though we could use a dice roller to cover that if it were an issue). We just keep a short text file to describe the game state, and it works quite well. Here's an example from the end of the first game we finished:
Turn 7 (Planning)
Initiative: Andrew
Warlord (Alexander - Green) : Channeling 9, Mana Supply 12, Damage 18 / Life 36
(Meditation Amulet) (Regrowth Belt) (Dragonscale Hauberk)
Warlord (Andrew - Blue) : Channeling 9, Mana Supply 15, Damage 3 / Life 36
(Ring of Command) (Leather Gloves) (Warhammer)
A4: (B) Grimson Deadeye (A+) (D:6)
B2: (G) Knight of Westlock (A+)
B3: (G) Knight of Westlock (A+)
B3: (B) Akiro's Hammer (L:2) (D:5)
C3: (B) Warlord (Andrew) (A+) (QC+)
C3: (G) Warlord (Alexander) (A+) (QC+)