I've tried a lot of Jamaican-style jerk seasonings in search of something really authentic, without too much luck. But recently, my friend Roger discovered Walkerswood Traditional Jamaican Jerk Seaoning, and I think my search is at an end.
Unlike so many other jerk seasonings out there, Walkerswood is a paste made up of hot peppers, scallions, black pepper, onions, salt, allspice, nutmeg, cane sugar, and thyme. It's made in and imported from Jamaica, and it's the most authentic jerk seasoning I've found.
It's easy to use - just rub some into the meat and let it sit a few hours (though overnight is best) before grilling or roasting. I've used it on chicken and pork so far, and it's AWESOME. (I'm considering making some beef jerky with it to see how it turns out.)
Walkerswood also understands that not everyone has a high tolerance for hot and spicy food., so they make a mild version that has the same authentic jerk ingredients with a little less hot pepper added to the blend. Don't get me wrong - Walkerswood idea of "mild" still might ring your bells if you are a complete pepper wuss, but it does have quite a bit less kick than the hot and spicy stuff.
Availability varies depending on where you live. I had never noticed it at all until just a little while ago, when Roger brought some back for me from a recent out-of-state trip. Since I've actually started looking for it, I've found it in a couple of ethnic markets (like Food Zone International on Belmont Avenue in Springfield MA) and supermarkets (I think ShopRite carries it in Enfield CT.) If you're a fan of jerk cooking, it's well worth the search.