Hmmm...with the internet nowdays you can get pretty much everything from around the world, which, IMHO has taken away some of the romance of getting 'country-specific' items. Anyhow, my recs are from a US department store chain here called Kohl's.
For US souvenir sake, I would check out their American Beauty line of cosmetics. They are made by Estee Lauder, and the line is modeled by the beautiful Ashley Judd. The names of the lippies like "Southern Belle" (my fave) and "Georgia Peach" and "California Coral" make for some nice keepsakes! Great quality makeup and a bit cheaper than most department stores (especially when they have sales--which include their cosmetics).
I would also check out the drugstores like Walgreens, Rite Aid, and the makeup sections of Target and Wal Mart. Lots of cheap treasures.