For me it will always be the Thoth. I think I actually got it a very short time before before I signed up, and couldn't make heads or tails of it, but it was here that I learned to love it (read: be obsessed with it!). I've had so many great teachers on AT, and in fact most of my education about it was right here (apart from books and stuff). But yeah, the Thoth for me was
all AT, and in time I like it so much I started to moderate it.
But beyond that, and I'm surprised it hasn't been mentioned, the
Dollar Tree Tarot. I don't like it and I don't have it, but if I ever see it anywhere, I'll make sure to buy it for At's sake.