I first stumbled across this stuff a few years ago in a slow wander through Whole Foods. I was intrigued - unlike almost all the packages around it, it only had a small label. The clear bag let you really see what was inside (a novelty for junk food), and it certainly didn't look like any popcorn I had seen before.
Little Lad's is apparently a restaurant in New York City and Maine (2 locations there) (The Phoenix has an interesting article that talks about the restaurants). And they're famous for their popcorn. Luckily, I don't have to make a trip up to Maine when I get a craving (and yes, I crave this popcorn like it's my job). (My, there were a lot of asides in this little paragraph.)
What makes this popcorn so amazing? It's not like anything else out there - it's tossed in a mixture of nutritional yeast and dried dill. Deliciously savory... and did I mention addictive? It sounds weird, and the name certainly doesn't help. The only problem is that you invariably end up with little flecks of dill under your nails - those can be a bitch to get out. It's messier than most popcorn too, so you may want to eat it was a Dustbuster nearby.
I used to find this at a bunch of different Whole Foods, but lately I've only seen it at my local Woburn shop. If your Whole Foods doesn't have it, ask if they can get a box. If you can't find Little Lad's, you can try making your own at home.