As a girl who is also awaiting the big question, don't ask for diamonds. If you ask for a colored gemstone, such as a ruby or sapphire (which I'm sure is what I'm getting), You can get a bigger rock for less money, and have that much more money to spend on te honeymoon, or wedding, or setting up a house.
I like your attitude!
Or, even better... ask for a moissanite. Most jewelers can't tell them from diamonds with the naked eye.