LEGO will have a total of four different free figures available (yet to be revealed), one for each day of the con.
To get one, you'll need to get in a line (usually outside behind the convention center) and receive a raffle ticket. Later in the day, LEGO will post the numbers of the winning ticket numbers and those people will receive the free figure of the day. (You must do this for each day.)
What's good about LEGO's system is that you have just as a good a chance to get a figure regardless of if you're first or last in line. Also-- it's free!
Also, they will have two exclusive sets priced at $39.99 each. One will be the 1966 Batmoblie (no image yet) and the other the "The Ghost" from Star Wars Rebels. There will be 1,000 of each of these sets available with 250 being sold each day.
Expect more images and announcements over the next few days.