Hey Spork. Well, I have tons of Snape-related theories. I don't think he's "good" or "evil". He's what I call "morally ambiguous". He'll serve either side, depending on what's in it for him. I think both sides were using him, and I believe the Dumbledore knew exactly what he was doing during the scene on the Astronomy Tower.
I'm going to be naughty and pimp my HP site here - check my siggy for a link. We do a whole lot of theorizing on HP matters, and that's where I met Scrubbo.
Nice talking to you.