PS3 lost exclusives:
KH3 - exclusive to DS
MGS4 - released ~ 5-6 months later on 360
360 lost exclusives:
Dead Rising 2 - Simultaneous 360/PS3 release
Ace Combat 6 - released ~5-6 months later on PS3
Wii lost exclusives:
Ninjabread Man - released ~4-5 months later on 360... joke ;)
Manhunt 2 - released 6-7 months later on 360