Not a sauce, but a persillade is a great addition to meats (and other things). A persillade is basically a mixture of chopped garlic and parsley (chopped almost to a paste). You can improvise on top of this base. Many people like to add chopped lemon rind. Anchovy is another good idea. You'll also want to add salt and pepper to taste.
Another idea is an Argentinian Chimichurri, which is a mixture of garlic, parsley, lemon, and oil. You can add vinegar and other things to suite your taste. Here's an example recipe:
1/2 cup olive oil
2 tablespoons fresh lemon juice
1/3 cup minced fresh parsley
1 clove garlic
2 minced shallots
1 teaspoon minced basil, thyme or oregano, or mixture
Salt and pepper to taste
Combine all ingredients and let set for at least 2 hours before serving.
Finally, in my book, it is hard to beat a roasted whole garlic clove. Take out the roasted cloves and use them as a spread (as is), or marinate them in olive oil, herbs, and goat cheese first.