SPOILER: There is a scene part way through credits: Marvel Character Thanos appears with The Other by his side. They are both looking down on Planet Earth with Thanos smiling, stating that they underestimated Earth.
The Marvel Studios and Paramount Pictures logos are seen within the Tesseract.
There is a scene after the credits: the Avengers are seen eating at a shawarma restaurant (the same one Stark mentioned at the end of the battle). This scene was originally only included in the US version of the film, but was included in the international DVD/Blu-ray release.
Part of the closing credits are seen amongst the equipment used by the main cast: Iron Man's armor, Captain America's shield, Thor's armour, Hawkeye's quiver, Black Widow's stingers, Dr Banner's glasses and Fury's gun.