The little blonde girl Elliott kisses when the frogs are released is Erika Eleniak, who went on to become a Baywatch babe.
Steven Spielberg has a cameo as one of the doctors when Elliot and E.T. are 'hospitalized' inside the house.
Gertie's line "I don't like his feet," was not in the script. Drew Barrymore just said it when she saw the puppet, and Spielberg kept it in the film. (DVD Commentary).
Two people actually supplied the voice of ET - Debra Winger and Pat Welsh.
Harrison Ford played the part of the School Principal but his scenes were cut. His wife at the time was one of the screenwriters and he visited the set regularly so Mr. Spielberg asked him to play the part. This rumor was confirmed in the 2002 20th Anniversary Limited Edition DVD book that came with the Boxset.
Inside ET's spaceship are several plant specimens. One of the plants is a triffid - from the movie Day of the Triffids.
This entire movie was shot in sequence. For people that don't know much about how movies are filmed, they are usually shot out of sequence (they might do the last scene first and the first scene in the middle etc). Spielberg did this so he could get the honest reaction from Elliot when ET left at the end.