I Am Legend
When Will Smith is in Times Square during the hunting sequence, he passes a billboard advertising a Batman and Superman team-up. Looks like lots of films like to drop in clues about their favorite caped crusadors. If you blink, you'll miss this reference.
Batman Begins
When Jim Gordon reveals to Batman that a new criminal has surfaced in the closing scenes of this movie, the Jokers calling card is shown, making it clear that he would appear in the sequel. But a closer look shows that the playing card was signed into evidence by someone called J Kerr. Short for Joe Kerr an alias the villain has adopted over the years, which means he might have been tempting Batman to bring him down for much longer.