1 cup sugar
3/4 cup water
Your choice of herb (ie: a fistful of mint, some rosemary, lemon thyme)
Bring the water and sugar to a boil in a stainless steel saucepan, stir until the sugar is completely dissolved, then toss in the herbs and clamp the lid on the pot. Leave it for at least 1/2 hour, then strain.
I usually let this mixture cool then pour it into freezer bags. I also usually triple the recipe, which means tripling the herbs (good use for all that mint spreading around your garden!).