Currently, my favorite store is Forever 21. Granted, some of the items are too young (I'm 24), but there are enough varieties in styles that I can always manage to find clothes that I like, that look appropriate on me.
Depending on your proportions, you may or may not be able to find pants there (they tend to go on the small, medium, large scale rather than numbers), but they usually have some cute skirts that will fit (not to mention dresses). Even when I weighed 165 pounds, I still wore clothes from there; it just might take some looking around. They have a webiste (
www.forever21.com) that you can browse through to get an idea of the kinds of clothes they have.
They range from casual, to club outfits, to outfits that I wear to work. Also, I think they're very affordable. Usually, I can get a garment for twenty-something dollars. Also, they have fun accessories there too.
Enjoy your night out!