Third Building...
The third building was 7 World Trade, 47 stories. It's generally known as the Salomon Brothers building - it was the corporate HQ of Solly before it was acquired and merged with Smith Barney, and still houses a lot of the merged firm. I have several friends who work there (all accounted for, thank God.) There are other occupants, including the main emergency management post for the City of New York (which had to be abandoned early on today.)
The building had been evacuated early in the day, although there might have been some firefighters in the lower floors - the building had caught on fire early on. I hope the firefighters got some warning and managed to get out before the building went.
The media keeps referring to the Twin Towers as "the World Trade Centre" - there are actually seven buildings that make up WTC itself. 1 and 2 are (or were) the Twin Towers. 3, 4, and 5 are fairly small buildings - all less than 20 stories, I think. Besides the seven buildings that make up WTC proper, there is (or was - I guess we have to get used to thinking of these in the past tense) a semi-underground shopping arcade between 1 and 2, a Marriott hotel that connects to the base of the Twin Towers, three different subway stations connected to the shopping centre, and a PATH station deeper below 2 (PATH is a separate subway system that connects NY to New Jersey - "Port Authority Trans-Hudson".) I've seen some reports that the hotel is gone, the shopping arcade and PATH station have got to be gone (the towers would have collapsed right onto them), and there's probably extensive damage - if not total destruction - of the other three buildings, along with nearby buildings like 130 Liberty (what was Bankers Trust Plaza, now a secondary building for Deutsche Bank.)