I am a huge fan of dresses. They seem to look good at any size, unlike jeans and pants which look much better on me when I'm fitter.
Button down shirts with darts/seaming are always attractive. Express sells the ones I've been wearing for the past fourteen years...(ugh, typing that made me feel old!)
When I was losing my baby weight and went up (then down) quite a few sizes, I went to Goodwill in an affluent town and found many good articles of clothing, including a Burberry handbag for $15, and several pairs of new looking work pants and sweaters from Banana Republic for $2-4 each.
With workout clothes, I tend to just get the Target Merona yoga pants/cropped pants/cami's and just wear a 3/4 sleeve tee with some kind of detail with it. If I'm working really hard (ie with a trainer and not just running or something) I have some champion stretch pants/workout tanks that I either purchased from Target or Kohls. If I'm hiking or something, I'll rock some ankle length stretch pants and a t-shirt dress. I'm all over the place
New clothes
