Warby Parker offers a curated selection of stylish, high-quality frames and a famous "Home Try-On" program where they mail you five pairs for free.
Zenni Optical is widely considered the king of affordability, with frames often starting under $20.
GlassesUSA.com and EyeBuyDirect boast thousands of styles, ranging from affordable in-house brands to designer names like Ray-Ban and Oakley.