Amazon has a $5 off coupon you can "clip" to your preorder for the 4-Disc edition of The Avengers. It's $34.99 right now, so with the coupon, the total will be $29.99.
Of course, new releases tend to drop in price as their release date approaches, so hopefully this will be no exception (releasing at $24.99 or $29.99 at BBY or Target is something to hope for ).
Amazon doesn't list a release date, but it's slated for 9/25 going by articles on various movie sites.
EDIT: Whoops, I didn't notice there's a Wiki thread now for coupons like this and someone else just posted this coupon in there. You can find the thread here.
Edited by Vigilante, 01 June 2012 - 08:30 PM.
Added link to coupon wiki thread