At least in America, there is a tradition of buying a promise ring for a serious girlfriend. Once parodied in the movie Baseketball, a promise ring is kind of a preamble to a formal engagement. Of course, promise rings for her make great gifts regardless of one's true intentions, just as long as she is allowed to keep it should the relationship sour. They can be personalized and are very reasonably priced, so be sure to check it out.
