Here are the places listed, many have been discussed in this thread, others are likely not the cheap ones.
PLACES TO SHOP
Coastal.com • Get your first pair free on select frames (shipping and handling, about $16, is not).
Eyebuydirect.com • Advertises glasses from $6.95, but $29.99 will get you a much cuter pair.
Madeeyewear.com • Custom frames that let you pick all the components — front, right temple, left temple, engraving separately. Test three free pairs with your prescription for seven days.
Spiffysociety.com • Starts at $95 for upgraded lenses; 30-day free returns.
WarbyParker.com • A leader in this niche. Known for simplicity of a free home trial — five pairs for five days free. Every pair you buy, means someone else in need gets a free pair of glasses.
Iristocracy.com • “Purveyors of uncommon eyewear.” Prices start at $245 for the frames no lenses. Uncommon doesn’t come cheap.
Mezzmer.com • Hands down, some of the best glasses descriptions online and great looking frames, too, starting at $69.95.
Zennioptical.com • Glasses start as low as $6.95 for prescription glasses, and it has one of the best interactive virtual try-on tools around.