The Alice in Wonderland costumes can be done with things you have. I posted earlier with links for that and for Lady Gaga. Also Instructables.com has lots of ideas for DIY Iron Man costume parts.
Instsructables also has lots of ways to do the make-up for zombie looks or for any look that would benefit from a few wounds–vampire victims, pirates, etc.
Click title for link at CNBC for a slideshow of the most popular costumes this year. Click the labels below this post for many more costume ideas. Have fun!