Han Solo
Played by Harrison Ford in the original trilogy, Han Solo is one of the most popular favorites. A pilot and sarcastic hero, he is a fun Star Wars costume choice if you want to find a character that you can "become" for the evening.
Darth Vadar
This is another great Star Wars costume choice. The outfit is cool and you get to carry a light saber. To find a Darth Vadar costume, you'll probably need to rent it. You can either buy a light saber at a toy shop or rent it with the costume. You don't want to skip this part. A light saber is one of the most important aspects of this costume.
Princess Leia
When the movies first came out, people wanted to look like Princess Leia. She is a fun character for those who love the first movies. You can braid your hair and wear the beautiful clothes. To make the character more believable, you may want to rent the costume
Yoda
Yoda is especially fun to dress up as. If you decide on Yoda as your chosen Star Wars costume, you'll need to develop his special way of speaking and you even get to carry a light saber. This is an elaborate character, so you will need to rent it and probably apply some makeup.
Luke Skywalker
Another classic character, Luke Skywalker is the ultimate hero. He fights Darth Vadar. If you arrive at the costume party or go trick or treating with someone who dresses up as Darth Vadar, you can reenact some of the fun scenes. Show up with someone who is playing Princess Leia and Hans Solo and you can almost recreate the entire movie.
Other Characters
Of course, there are plenty of other characters and you can also find a costume based on them at costume shops. There's Padme Amidalla, Jar-Jar Binks, Chewbacca, Obi Wan Kenobi, etc. Pick a character you can have fun with.