When Marilyn Monroe said diamonds were a girl's best friend, she knew what she was talking about. The sparkly stone can incite just as much ardor and devotion as the man down on his knee proffering it up . . . and can look a whole lot more exciting! In honor of today being National Proposal Day, we're rounding up some of the most gorgeous rings we've crossed paths with recently. Whether they're jaw-droppingly stunning or simple and sweet, these are the rings that'd make us say yes again, and again, and again.