I have found a few brands of canned baked beans that need no doctoring at all, but they're usually on the high end of my food budget. If I'm dealing with standard baked beans, I'll add mustard powder and ketchup at least. Brown sugar is a good idea, too, but I try not to add too many sweet ingredients without using a few tangy or savory ones, too.
My favorite way to serve canned baked beans is sometimes called "cowboy style". I'll add cooked ground beef to the beans and top them with bacon strips while they heat up in a casserole dish.