drugstore.com

Full review
drugstore.com is one of the best online retailers, and I use them at least twice a month to cover my pharmacy needs.  I have used almost every service they offer, including fulfilling prescription drugs, ordering contact lenses, purchasing every day items, and even buying food.  Overall, I would highly recommend drugstore.com for most of these services.

1.  Filling prescription drugs:  It was relatively easy, but still not as easy as going to Walgreens or Duane Reade, if in Manhattan.  You can either fax the prescription or have your doctor's office call it into their toll free number (if this is still the case from the last time I filled a prescription).  It arrives within a day or two, but when I'm sick and need my prescriptions immediately, it's not recommended.  Their service is recommended for filling maintenance drugs you get regularly (i.e. blood pressure meds, birth control pills, etc.), which you can even get on auto-delivery fit to how often you need them replaced.

2.  Ordering contact lenses:  It's not the best option but there are good deals, and definitely much less expensive than at optometrists' offices in Manhattan.  You fill in your prescription info for each eye, choose the number of boxes, and type in your doctor's office info so they can confirm your prescription.  I use this service to replace my contacts on autodelivery, and it saves me time and money.

3.  Purchasing everyday, non-prescription items:  It is so easy, and there are a variety of reasons ordering online than going to a local pharmacy.  These include convenience, privacy, and being able to select from a wide inventory of products that are not all available in my local pharmacies/bodegas (compared to Duane Reade's inventory, it's amazing)!  With non-prescription orders over $49, shipping is free, and you get 5% credit applied to your next purchase with eligible purchases (and most things seem to be eligible).  An added bonus is that you get credit for purchases on beauty.com as well with their "2 sites, 1 bag" policy.

4.  Purchasing good/snacks:  Not recommended.  Things get broken, smooshed, and it just doesn't hold up that well.

While I know most pharmacies and drugstores have promotions to save you some money, drugstore.com is the only one that consistently gives you the 5% credit so that over the course of a year, you can save hundreds of dollars on items you'd buy anyway, like toothpaste, paper towels, soaps, detergents, and all your personal care, and household needs.