FFK :
Squat, squat, squat, squat !
Squats will burn huge amounts of calories, make you stronger overall (in your abs and back), and give you an attractive muscular butt and legs. There is zero reason to worry about getting "too big" ; that doesn't just happen, you have to work very hard to get big and if you don't want to, you won't.
Good article on girls squatting :
http://www.stumptuous.com/cms/displa...le.php?aid=123
and BTW that whole web site is good for women's weight training :
http://www.stumptuous.com/cms/index.php
Here's some inspiration (small girl who does all the olympic lifts) :
http://www.youtube.com/profile?user=stiznel