I've never been one for fanfic (other than the wonderful CBB, of course!) but I clicked a link to Blood Magic, as recommended by circe_tigana and as such have spent the past 100 hours reading it through. It's very good. The male characters have a worrying disposition to acting like an Oscar Wilde-type fop, and there's underlying sexual tensions between just about everyone but the developing relationship between Snape and Harry is well done.
So now I've finished reading that (and encouraging you to read it too!) I need something else to fill it's place! Something long, and something good please, no Mary-Sue's or bad writing!