Congrats on finding a great girl!
I'm pretty opinionated about the diamond topic - a lot of my guy friends have come to me for advice on this
Personally, I could have done without a diamond - I'm not really the traditional type. My husband wanted me to have one. Some woman would only want a diamond because they are more traditional. Sounds like your girlfriend fits into this category?
I am in the wedding business (photographer) and I can always tell when a man picked out the setting without the woman because its a lone solitaire. Not that there is anyting wrong with that, but I think most women want a unique setting that reflects their personality.
You have a couple choices - one guy friend presented his fiance with a loose diamond in a box while on a romantic date and they went to the store and picked out a setting together. That was a win/win because there was still the element of suprise but she got to pick out her setting.
I gave my husband a general sense of what I wanted (an antique style ring) and he got me a setting from the designer Tacori (
www.tacori.com).
I think that you should at least attempt to get a sense from either her or her friends as to what type of setting she would like. Chances are she has shared this with her friends if she thinks you are going to propose. If you have an engaged friend you could say "what do you think about Sally's ring?" and see what she says. If she say "oh, I like it, but I'd like a more modern setting" or if she says "I love it, but the diamond is set a little high" you have an idea of what she is looking for.
Since you can't return a setting, I think its worth doing some major research before springing for one. You could also purchase an inexpensive temporary setting for a few hundred dollars and then let her choose a new one sometime during the engagement.
I also highly reccomend platinum as a metal. As with most things, you get what you pay for and platinum is expensive, but the strongest metal.
Finally, from the second you bring it home - INSURE IT!
LN