Target is advertising a bunch of Marvel Lego sets this week. It doesn't look like any of them are on sale though. You also get a "Free" LEGO Teen Groot keychain (a $5.99 value) with LEGO Marvel Super Heroes purchase of 14.99 or more.
Toys'R'Us is advertising some Lego sets for an Easter sale. There's at least one really good deal in there. They also have some Clearance items.