I do a lot of online shopping, so I thought it might be useful to list some of the e-tailers I use and would recommend here. I'm not affiliated with any of these, and receive no remuneration if you click on the links to the websites.
Content Organic & Natural
Excellent shop with natural/organic luxury brands. I buy my rms Beauty products here, and they also stock Strange Invisible Perfumes (if you're curious, they sell samples of the scents for £2 each, which is a good way to try.) I also love the Dr Alkaitis skincare, and Stem Organics skincare, which has high performance ingredients in excellent bases. I'd also recommend Evolve products, which are very reasonably priced, and Inika mineral cosmetics (which don't give the weird shiny/itchy thing I experienced with a leading mineral brand.) Free UK delivery over £50.
Luxury and hard to find cosmetics. I buy Rouge Bunny Rouge here, they also sell Hourglass, and will soon stock Edward Bess. Free UK delivery over £50, and they often have very nice GWPs.
Stock a huge range of hard to find brands, including Shu Uemura, the website is easy to navigate and they also offer a 5% cashback loyalty scheme and free shipping on orders over £50. It's worth signing up for their emails, as they quite often have special offers and discount codes.
Beauty Bay sell Classified Cosmetics ERA spray foundation, and I'd challenge anyone to find a foundation that wears better than this. It's my first choice when I really need my make-up to last all day, particularly in hot/humid weather. They sell Morrocanoil hair serum, which is a bit heavy for my hair but apparently a godsend for thick or very curly hair. They've also got the Twilight cosmetics in, if that floats your boat.
For Nubar, one of the best nail polish brands available, in my opinion.
Excellent indie pigment maker. The Pixie Epoxy primer is a must-have. Prices are very reasonable, samples are generous, and they ship internationally, free with orders over $20.
Based in Ireland, but also ships internationally. Stocks Ellis Faas and Julie Hewett, as well as other niche luxury brands. Shipping has been very fast on both occasions I ordered from them, beautifully packaged and with relevant samples.
I buy my Addiction by Ayako from here. The prices include shipping fees, and you get free express shipping with orders over $150. I've found the service to be fast, friendly and helpful.