What is your hall theme going to be? The key is to do something easy but inexpensive. You definitely don't want something that takes a lot of intricate cutting or coloring, as you'll really hate the idea after, say, you've done 10 of them. I did a superhero themed hall when I was an RA. The girls had Wonder Woman bages with their name and the guys had Superman S's.
Some other people did: Picture frames (and used his digital camera to take pictures of the residents when they moved in, which he then put in the frames), comic strips (it was a Peanuts themed hall, color copies were very useful and easy!), one hall was bowling themed so they had bowling pin paper cut-outs and bowling balls.
What do you like? What would you find interesting in a theme for your hall? Do something on that, that way you'll enjoy planning it out!
-------
So when you're happy (Hurray!), or sad (Aw!),
Or frightened (Eeek!), or mad (Rats!)
An interjection starts a sentence right.