if money's a little tight (which it is for me and i think most of us), check out outlet malls, ann taylor loft and casual corner/petite sophisticate. get a nice conservative suit -- pant suits are fine -- basically just no funky or way too bright colors, too short skirts, etc. loafers work for pant suits, but skirt suits seem to require heels. also, if you opt for the skirt suit, go on the safe side and wear hose.
shirts aren't a big deal -- look for cheap options at places like tj maxx. actually, this is where it's cool to be a woman because we can have more fun with our tops. do the conservative suit, and you can go for the sort of funky shirt. personally, i hate oxford style shirts, so i don't wear 'em. they can look really cool and professional, though, so if you dig 'em, wear it. sweater tops also work, as do those tank top shells. again, check out places like ann taylor loft and casual corner for ideas. the color is not a huge deal. mainly, just go for something that looks good on you.