There are many options available to you when preparing a tomato sauce. Try replacing the oregano with a bay leaf or some basil. Try a finely diced pepper or even cilantro in place of (or in addition to) the onion. Another idea is to look around the grocery store at what types of tomato sauces there are and take a crack at incorporating some of those varieties in your own sauce. Vodka and cream are also popular flavorings these days. Be sure to steam off any alcohol after adding vodka to tomato sauce.