I've used Netrition several times over the past 3 years and they are excellent. I've never bothered with the Atkins site as it is very pricey. Netrition offer about the best discounts on most products (including Atkins bars).

The parcels arrive quickly. Be warned though if you aren't used to ordering from abroad. You'll have to pay the courier an additional amount for VAT and clearing customs. Since mail order stuff from the US is tax free and usually much cheaper than UK I don't find it too much of a hardship.

Incidentally, does anyone know why supplements are so much more expensive in the UK? A few of the standard ones aren't bad here if you buy generic ones. But stuff like Alpha Lipoic Acid and Co Q 10 are a quarter or even less of the price in the US. I was doing a big order at vitaminshoppe and out of interest looked at Solgar B-100. It's $17 at Vitaminshoppe but £40 in the UK. Same product, quantity, make!