TK maxx have some good ones.Loads of pretty polly etc. Call me a trotter, but I got some fab hot pink leopard print ones there last winter for £4. I look forward to the day post-pregnancy when I can wear them again without my middle looking like the join in a string of sausages.
I am an 'interesting tights' fiend and I have had good pairs from:
Wolford (in the HoF sale - still expensive but they do last well); Accessorize (mega cheap in the sale); TK Maxx - they often do interesting tattoo patterns etc; M&S - some awful ones but the Autograph cashmere mix are good (though plain) and they do have at least one nice lace pair at the moment; Topshop; Tie Rack (I don't think they do many pairs but I got a gorgeous pair a few weeks ago).
My Tights have a fine selection at a range of prices. Stockings HQ do stockings and tights. (Though don't join their Facebook page as it attracts some very strange types!) I tend to wear 'interesting' tights especially the woolly ones or seamed stocking for the (rare) occassions I now go out dressed up. Got some very nice ones from M&S last year but haven't looked this year. H&M had some fun ones yesterday.
I hate hate hate John Lewis tights. Not much help about where to get nice ones, as I live in M&S black opaques (Jonathan Aston for specials), but just to say that my John Lewis tights always seem to have a funny elastic balance - if the legs fit the waist just falls down and the crotch ends up around my knees.
I second Accessorize.
It's also worth browsing on the figleaves outlet from time to time - not much there now but sometimes there are fab bargains.