Hanging Gardens of Babylon, Nebuchadnezzar to his homesick wife. Bottom line, if your gift is ranked among the Wonders of the Ancient World, you win at presents.
Statue of Liberty, France to USA. Giving someone a work of art as a gift is a stressful endeavor. Will they like it? Where will they put it? In this instance, France nailed it, giving the US a present that would later become iconic in everything from our postcards and placemats to our post-apocalyptic landscapes.
Fire, Prometheus to Humankind. Zeus was less than sympathetic to Prometheus's desire to share fire with the humans, in turn giving the titan the gift of a new residence and a perpetual liver-massage courtesy of a Caucus mountain eagle.
Trojan Horse, Greeks to Trojans. This is sort of a worst gift/best gift situation depending on which side of the Trojan War you fell on.
Savannah, GA William T. Sherman to Abe Lincoln. December, 1864: Washington had had no word from General William Sherman and tensions were growing before the famous general wired the president to tell him "I beg to present you, as a Christmas gift, the city of Savannah, with 150 heavy guns and plenty of ammunition, and also about 25,000 bales of cotton."
Taj Mahal, Mughal emperor Shah Jahan to his wife, Mumtaz Mahal, who died giving birth to their 14th child.
Miniatur Indien Taj Mahal.jpg, By Anonymous ( (2011/1)) [Public domain], via Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Miniatur_Indien_Taj_Mahal.jpg