From 9to5Toys.com:

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Walmart continues to offer the $50 iTunes gift card for $40. That is 20 percent off and the lowest price yet. The card comes immediately through email, and it counts toward free shipping on other items.  It may also be a good way for our International readers to purchase iTunes gift cards for United States music.

For those near a Best Buy, order three $10 gift certificates for $25 and with a free reward zone account, that drops to $22.