Well first off, finish the last episode
Afterwards, go watch the move, "The End of Evangelion." It's basically a redo of the last two episodes. It wraps the series up very nicely (and if you thought the end of evangelion was crazy, wait till you watch the movie). You could also watch "Death/Rebirth," but it is basically just a retelling of the whole series in a very wierd order. And unless your a die-hard fan (like me
) your probably not gonna find it very interesting.
Afterwards, there isn't really anything else, anime wise that is. If you want to get even more Evangelion, I suggest you read the manga. It is pretty interesting because while it does follow the same general story, it has quite a few variations to it. Characters are portrayed a little differently, and there are different things that happen.
The reason for that is because (long story short) the anime is Hideo Anno's (the director of the anime) version of the story, while the manga is Yoshiyuki Sadamoto's (the character designer) version of the story.
*EDIT*
I completely forgot until just now. But you should probably know that even though the manga has been going since 1995, it still isn't finished, Sadamoto works on it at a snail's pace. It's currently at volume 9 now, and I believe it's finally gonna wrap up in volume 10, or 11 or something.
Just be warned, don't wait for each new release of the manga, since it literally takes years for them to come out.