Gee, I buy EVERYTHING on line, even groceries from my corner store sometimes
GNC carries a pretty good selection of the Atkins bars and muffin mixes at a decent price so I usually buy those in person.
I get my LC vitamins (so far Atkins brand, I may branch out and try others in the fall) and basic LC bakery items from vitacost.com.
After someone here (over in recipes I think) mentioned SF Chai I just did a big order with alacarb.com. Among other stuff, they carry the DaVinci syrups & concentrates (the Chai is divine) and a bunch of stuff by LowCarbSuccess. I had their pizza crust and it was super so I order three more for treat nights. They are 3g of net carbs per slice, plus the toppings of course. It might be OP but it's still more carbs than my usual dinner... I also got the LowCarbSuccess FlaxMeal hot cereals to try. I had some as a snack yesterday (90F out and I just HAD to try my new goods

). It was yummy (needed SF maple syrup) and so filling I almost didn't have supper.
All the LC stuff is moderately pricey but it is the only game in town. I usually buy a selection of things so I can change my meals up from time to time so I don't get bored. I don't use it everyday necessarily. Also, the online prices are cheap enough (and they actually have it instead of driving all over the place!) that it makes up for the shipping costs. I usually wait and do a big order to save on the shipping rather than doing a bunch of little orders.