you should check out the jamis line of bikes. with Jamis it seems you really get a lot for your money. their 48cm runs small and they also make a 44cm bike in an aluminum frame with carbon seat stays and a carbon fork with shimano 105 components that runs about $1200. the 44 even uses 700c wheels which is cool because you don't limit your choice in tires, tubes are easier to find, wheel upgrades are easier and if you get a flat on the road and someone stops to help you, their spare tube will fit your bike too

i am also very petite and found that the scott contessa in the 47cm fits most small women great, they run a shorter top tube. the jamis however puts carbon seat stays which add comfort and dampen the harsh feeling of the aluminum frame, especially on the smaller size bikes.

i found the the giants run very long in their top tube, so if you have a shorter torso/arm combo and longer legs you might feel really stretched out. The giants also run a longer wheelbase which affects the handling. some people like it, others don't.

The best thing to do is get out there and test ride stuff to find what feels most comfortable for you and remember it is easy to change your stem/handlebar combo to dial the fit in.