Worms Open Warfare 2 (Single-card, Multi-card, or online)
Clubhouse games (Single-card, Multi-card, or WFC)
Fifa 08 (Single, Multi-card, or WFC)
Contra 4 (Multi-card)
Glory Days 2 (Multi-card)
Mario Kart (Single-card, Multi-card, WFC)
New Super Mario Bros (Single, Multi-card, or WFC)
Brothers in Arms (Multi-card)
Metroid Prime Hunters (Single and Multi-card, or online)
EDIT: Forgot to mention Mario Party DS. It's very fun single-card, although I'm not sure if there is an option for multiple DS carts.