Could not find the original thread, there was a discussion around the Canon 580exII and free Targus backpack. Just checked this out today.
American Express promo - charge >$500 to your card at Sim Lim or Funan and you can redeem a Targus backpack. (I got a Targus New Urban backpack). Must redeem on the same day. For more info see: selects.com.sg
Canon 580exII - there is an offer of $599 for 580exII when you purchase the 50D. Some of the shops will let you buy the flash alone at this price .