I usually prefer a marinade as well. Here is my jerk marinade, directly from my 'cookbook'.
4 scallions, chopped
2 habanero chiles, seeded and finely chopped
splash dark Jamaican rum (like Appleton Estate)
Juice from 2 limes
1 Tbs allspice
¼ tsp nutmeg, freshly ground
2 tsp thyme
1 tsp cinnamon
2 Tbs ground coriander
2 Tbs ground ginger
1 Tbs cayenne
2 tsp onion powder
2 tsp cloves
salt & pepper to taste
Combine the scallions, chiles, rum and lime juice in the carafe of a blender and process until smooth-ish, then add in the rest of the spices. Makes enough for 8 whole legs of chicken, or 2 pork shoulder roasts, or perhaps a large roast and a couple tenderloins.
The real heart of the jerk flavor is allspice, nutmeg, thyme and cinnamon. So focus on adjusting the quantities of those ingredients until you find a balance you like, then go off and play with the support flavors. Obviously, you can play with the heat by not seeding the chiles, or simply adding more of them; a truly proper marinade would probably have double my amount of Scotch bonnet or habanero, Mrs Tif cannot abide strongly Scoville'd out food so this is my compromise.
One final tip; it's expensive but worth the effort to seek out hardwood charcoal from Jamaica. They use wood from allspice trees (they call them pimentos in Jamaica) to make their charcoal, and the smoke is unlike anything you can find from another source. If I don't have pimento charcoal, I'll throw a couple handfuls of whole allspice berries onto my fire. It's better than nothing, but not nearly as good as pimento wood. You could also use wood chips from fruit trees, like apple.