Breif summary from
http://septterror.tripod.com/the911basics.htmlWTC 3: The Marriott World Trade center hotel. The 22-story hotel originally was the Vista when Hilton opened it in 1981. It was destroyed by debris from the collapsing towers.
WTC 4 and 5: The "Plaza Buildings" each had nine stories, with WTC 4 on the south and WTC 5 on the north. Both buildings were heavily damaged and were torn down in 2001-2002.
WTC 6: The US Customs House; eight stories. Severely damaged in the attack and demolished by construction crews in 2001-2002.