Salt, pepper, olive oil, and an acid--i.e., lemon or lime juice--are things I never tire of, especially when goosed with fresh herbs like basil, oregano, marjoram, tarragon, and cilantro. It's the herbs that dictate the flavor profile. As for sauces, I like to have an inventory on hand of several different barbecue sauces (you can see my favorites at www.grilling4all.com, or check out my book, Sauces, Rubs, and Marinades.)
On fish, I enjoy mustard and/or wine-based sauces.
This is a little off the topic but, one of the things you can do to add moistness and flavor to poultry and pork is to brine it. The brine can flavored with various herbs or spice mixtures or even citrus. Soak the pork/poultry in the brine in the refrgerator, dry it off and cook. Adds great flavor and moistness.
My basic brine is 1 gal water, 1 c sugar and 1/2 c kosher salt. I add flavorings like orange or lemon or garlic or a premade seasoning mix like jerk seasoning (or any combination of herbs and spices that I wish to use to create a specific flavor profile) to the brine while it is cooling to allow the flavors to develop while the brine is cooling.
I like the idea of brining shrimp. Will need to play with that one. Thanks