Actually, NBC/MSNBC led the call for Gore, with CBS and CNN following closely thereafter. Fox might have been early, too. ABC was the only one to call it after the polls actually closed, waiting til 8:02.
Interestingly, Fox never retracted the call for Gore until about 2 am; they were the the first to call it for Bush, at 2:16 am.
Note the following excerpt from Nader-voter David Kopel (http://www.davekopel.com/Terror/Fiftysix-Deceits-in-Fahrenheit-911.htm):
In fact, the networks which called Florida for Gore did so early in the evening—before polls had even closed in the Florida panhandle, which is part of the Central Time Zone. NBC called Florida for Gore at 7:49:40 p.m., Eastern Time. This was 10 minutes before polls closed in the Florida panhandle. Thirty seconds later, CBS called Florida for Gore. And at 7:52 p.m., Fox called Florida for Gore. Moore never lets the audience know that Fox was among the networks which made the error of calling Florida for Gore prematurely. Then at 8:02 p.m., ABC called Florida for Gore. Only ABC had waited until the Florida polls were closed.
About an hour before the polls closed in panhandle Florida, the networks called the U.S. Senate race in favor of the Democratic candidate. The networks seriously compounded the problem because from 6-7 Central Time, they repeatedly announced that polls had closed in Florida--even though polls were open in the panhandle. (See also Joan Konner, James Risser & Ben Wattenberg, Television's Performance on Election Night 2000: A Report for CNN, Jan. 29, 2001.)
[...]
Even if the premature television calls affected all potential voters equally, the effect was to reduce Republican votes significantly, because the Florida panhandle is a Republican stronghold. Most of Central Time Zone Florida is in the 1st Congressional District, which is known as the "Redneck Riviera." In that district, Bob Dole beat Bill Clinton by 69,000 votes in 1996, even though Clinton won the state by 300,000 votes. So depress overall turnout in the panhandle, and you will necessarily depress more Republican than Democratic votes. A 2001 study by John Lott suggested that the early calls cost Bush at least 7,500 votes, and perhaps many more. Another study reported that the networks reduced panhandle turn-out by about 19,000 votes, costing Bush about 12,000 votes and Gore about 7,000 votes.