Ric-El, I second the head-band costume. That one is my favorite as well.
I've got a small run-down of some of her costumes at
http://superman.nu/supergirl/costumes/ but the one that lastkryptonianhere mentions isn't shown. So here it is:
There are a lot more costumes - I remember when she changed her costume a few times every issue, and people sent in their own suggestions and designs! That was great fun and the comic was more like a teen fashion mag.