Business Casual?

Just started a job where the dress code is majority business casual. Ladies... Where do I shop for this? I have a few outfits I've collected over the last year or so. I don't want to look stuffy, I'd say my style runs along the mod/hipster/geek chic line. I love ModCloth, but it's pretty pricy, I like H&M but it seldom looks good on me.  I'm comfortable in dresses or pants, but pretty exclusive to flats. I just cannot do heels, try as I might. Any advice?