My dds find stacks of nice things in charity shops in Oxford. Nearly new dresses from East, Boden, all sorts, for £10 or less. Dd1 recently found a really lovely dress to wear to a summer wedding - it looked new - for under £10.
And, dare I say it, having looked until she was in despair for a brand new dress for her own civil wedding last year, she finally found a beautiful silk one in a charity shop - truly gorgeous colours and fitted like a dream - for under £20.
Having said that, I think their charity shops get a lot more good stuff than the ones around here!
Dd2 is also a great one for sales. She will find e.g. really good leather boots for say £35, marked down from £120+.