A straight guy's good friendship with a great girl who is also straight is technically a relationship already in itself. It builds upon itself naturally. From just having this good friend status, I guess it just means that either side is unhappy, if one of the two wants something more.
The great advice I got from one of my "girl" friends is to just have an open mind for candidates and not just focus on one person. It's something that will just happen unexpectedly. She's happy to have enough in her life already and with her boyfriend, they seem to be on a break right now. I asked her out and she accepted, but it's only because I see her personality as being someone who likes to spend quality time with an individual. It's great to be friends with her.