Best Buy has $50 iTunes gift cards on sale from May 11 until May 17 for $40. Pick one (or many) up and save 20% on all your iTunes store purchases including music, movies, TV shows, books and even software at the Mac app store.
Source: iPhone in Canada
Update: It seems like iTunes gift cards are on sale every week, this time they are at Walmart. So hurry on over to Walmart to get a $50 iTunes gift card for only $40 from June 6 until June 14.