My three favourite saisons, in no particular order:
Dupont - as others have said, the standard by which other saisons are judged. Delicious refreshing goodness.
Tank 7 - have only had this a couple of times, but damn it made an impression. Again, refreshing, and bursting with flavour.
Saison Cazeau - made with elderflowers, smells amazing, tastes spicy and sharp.