I'll kick off -- having broken my leg I'm in no position to nip to the shops, so have plenty of time to evaluate mail order services.
Hall of Fame:
Jelly and Bean. Marooned in bed, I've been teaching dd2 to read, and these books are great. They send them off speedily, and send you nice personal emails if you have queries or special requests.
Harry Duley have lovely clothes -- delivery times aren't that fast cos they pretty much make the items to order, but they will also do special requests (eg. extra long trousers) and v. friendly and personal service.
Sweaty Betty. Expensive, but the stuff arrives quickly, which is important when the only thing you can fit over your mahoosive leg brace is baggy yoga bottoms. Nice and long, too.
Roll of Shame:
Bldy White Stuff. They keep sending me frcking emails advertising all their lovely clothes. I fell for it and ordered it two weeks ago. Despatched 10 days ago (allegedly). Have chased repeatedly, they keep blaming Royal Mail and saying they'll get back to me, then don't. Meanwhile they have of course charged my debit card, but no sign of any clothes or phone calls to explain where said clothes are. Bggers.
Any others to recommend or avoid?