I found this recipe for Harissa on moroccanfood.about.com. It goes very well in Jenise's Merguez sausage recipe.
100 grams dried red chile peppers
3-4 cloves garlic
1 tsp salt
1 tsp ground cumin
1/2 tsp ground coriander seeds
1/2 tsp ground caraway seeds
2-3 tsp lemon juice
olive oil (if necessary)
1. Cut the chiles in half and remove the seeds. Soak the chiles in very hot water for 30-60 minutes.
2. Drain the chiles and gently squeeze out the excess water. Grind the chiles, garlic, salt, and spices to a paste. Add the lemon juice and just enough olive oil to moisten the harissa. Add more olive oil if you prefer it thinner.
Store unused harissa refrigerated in an airtight container. For longer storage, top the harissa with a little olive oil before covering.
This technique is identical to the way that Thai red curry paste is made--only the spice ingredients are different. Traditionally a mortar and pestle is used for the grinding, in which case you'd start with the dry ingredients (the salt and spice seeds), and once you've pounded them to a powder, you'd add the chiles and then the garlic. A food processor or blender does the job, too, in which case I recommend grinding the spice seeds in a spice grinder first, then throw everything in the processor/blender and grind until smooth.