I love ASOS as well, though it's always good to be sure of your size. Topshop, Urban Outfitters, Primark, French Connection... most high street stores. For dressier events though I've found a really great website where you can hire dresses and they're actually designer. Its pretty good: www.wishwantwear.com
Would recommend for anyone with a special party/ event to go to!
I only shop in sales and I rarely buy clothes. I try and get good quality bargains rather than loads of cheaper clothes which won't last long. For basics, I only buy cheap - no one can tell one white t shirt from another.
Topshop (mainly sale only), Primark, H&M, Miss Selfridge (mainly sale only), new look, river island occasionally. Pretty much anywhere though, I have gone waaay past my shop snobbery days - if I like it and it's cheap I'll buy it.
I buy most of my clothes from vintage shops, charity shops, car boot sales and jumble sales - most of the time you can get nice clothes for a fraction of the price, and a lot of them aren't current season, so it's not likely that anyone else will have the same items as you. I also like that I am saving an item from landfill by buying second-hand. Shoes I buy new - I love Rocket Dog shoes, and Etnies, Vans and Osiris skate shoes, so I usually either buy from TK Maxx, Schuh, or from the Interwebnets. Make up if bought new from ebay, or from Boots when they do good GWPs ( gift with purchase) during Christmas and summer-time.
Accessories I tend to buy vintage too, or from charity shops/jumble sales again, though obviously I buy socks, and undies new - usually from La Senza, Gossard stockists, or Figleaves. I think a decent bra is well worth investing in, as it can change the whole shape of your body - makes you stand up straighter, shoulders look squarer, and breasts are obviously supported and look pert, thus your outfit will look better on you