Also, I think you should make the actual proposal at least somewhat memorable. I don't mean be extravagant, but give her a story to tell her girlfriends and your grandkids. I'm sure Ladypine loves telling how Tallpine proposed because it speaks to his style.
Be original - asking her in a restaurant has been done a million times, no matter how you present the ring.
Don't be goofy about it - hiding the ring in food or other nonsense.
Be yourself - do try to draw on your better traits, but don't do something out of character. She knows you and knows what she's getting herself into, so be yourself. And it should be geared toward who she is too. Don't do anything that's going to make her uncomfortable. I would be utterly mortified to have a marriage proposal splashed on a billboard or over loudspeaker but some women might find that romantic.
Also, do NOT say, "I know you want to get married while your mom is with us so I thought I'd propose now." A) She doesn't want to think about her mother dying during what's supposed to be one of the most memorable moments of her life, and B) She wants to believe that you're proposing because you love her and want to spend the rest of your life with her, not because of some outside influence, even if it is to make her happy.
And you do realize that us girls are gonna wanna hear all the details when the deed is done, so don't forget about us!