Matanuska thunder fuck. If you can find it, will fit in the "rare and harder to find" catagory. I was recently gifted a small bud to enjoy. Wowee! Very potent and super trippy. I was glad I hadn't taken a second toke. I can't say with certainty it was the real deal, but whatever it was, the taste and buzz fit the general discriptions given by people who claim to be in the know. Not an everyday smoke for the likes of me, but certainly a unique strain to puff on once in a while.
The guy who gifted me didn't own the plant. I tried like hell to get a clone down through the chain of custody, but no dice. I've been looking at Dr. Greenthumb's seed version with high hopes and also a healthy dose of reality. I'd love to hear from someone who's tried them out. If they came close to the real deal, they would be worth the dough.