I have to recommend this fanfiction trilogy because it's the best thing I've read in ages. It covers the snakey side of things (so lacking from JK's point of view), adds in the youngest years (who don't really seem to exist in the last few Potter books) and fills in a lot of character background to the usually one sided inhabitants of Slytherin house. So much of the Potter books take place in the Gryffindor Common Room and as I'm a Slytherin girl I can't help but wonder what's going on down in the dungeons instead.
Largely humerous, sometimes tragic and thoroughly entertaining I couldn't stop reading until I'd read the whole lot. The story is largely told by the "smallest Slytherin", Violet as she arrives in the wizarding world and tries to make sense of being a snake in a very anti-Slytherin world.
The rest of the houses and professors feature heavily, along with the inhabitants of Hogsmeade, Diagon Alley and the Death Eater camp.
I really can't recommend it highly enough. Beautifully written, lots of chapters, plot twists and mysteries to enjoy...and loads of fabulous illustrations too. I want to crawl into it and live there.
...for the SSHG crowd, there's several hints of a future along the way too. Lots of SSHG fics jump straight into post Hogwarts secret admirations between the two and you reel a bit and wonder how the heck happened. My imagination is now going to assign this fic as pre-SSHG canon.
Alas, the negativity from the anti-Snape (there's people who are anti Snape?! How dare they!) anti-Slytherin crowd before the release of book 7 made the writer of these wonderful fics abandon her plan for a fourth fic,
Suddenly Severus but I shall live in hope of her picking it back up again.
I wish I'd found this at the time it was written, having struggled as a determined pro-Snape Slytherin sympathiser since book one who was still insistant that things would work out after reading the last pages of Half Blood Prince.
(fic illustration by BJ Rosen which remains the property of the author and the illustrator, but which I'm using as an insentive to go read the fics. The little girls in the picture are jokingly referred to as Snape Snugglers.)
The Smallest Slytherin
http://cda.morris.umn.edu/~webbrl/SmallestSlytherin/ An Obedient House
http://cda.morris.umn.edu/~webbrl/AnObedientHouse/ Salazar's Orphans
http://cda.morris.umn.edu/~webbrl/SalazarsOrphans/