That is the question.  I'm wondering whether or not I should come out to my friend.  She's very liberal and supportive of the GLBT community and we've known each other since we were 6.  She's actually the one who converted me from my conservative upbringing.  If/when I decide to transition she's definitely the one I'll be telling first.

The thing is, when I discovered Underworks binders a few months ago and excitedly sent her a link about it, I learned how much girls like their chests and can't imagine why I would want to flatten mine.  Awkwardness ensued on my part, but she said "don't feel awkward!  Just because I don't get it doesn't mean it should discourage you.  If it's what you want to do, then do it! "  That made me happy, but I still felt awkward and dropped the subject.

Since then she told me about the transgender character she wanted to dress up as for a convention, and she joined a group on facebook supporting legislation to protect transgender people from discrimination.  So I'm wondering if she suspects it and is trying to get me to tell her, or if I'm just hyper-aware now.

I'm almost positive she would be supportive, but I'm still in a stage of wondering if I'll actually go through with anything/whether it's all in my head/something I'll grow out of, etc.  (I'm very self-doubting.)  I'd just hate to tell her before I'm 100% sure and then never go through with anything and feel awkward afterwards.  Suggestions?

I say tell her.  You may have one in your corner. 

to tell! that is my answer
it's great thing to be able to share even your thoughts and doupts with a close friend , if you trust her enough , don't hesitate , sometimes it helps when you say things out loud , she might even help you figure out everything
good luck and i hope it works to the best

Really?  I think I want to tell her, but like I said, I'm not sure if I'll go through with anything.  I trust her but she's got her own problems to deal with, so I don't want to bother her with this if I'm not sure it's going to amount to anything.  I'll think about it.  Thanks for the input! 

I'm guessing she already knows, especially if you were sending binder links. Several of my friends knew and I never did anything that overt. She's probably waiting for you to come out, and dropping hints to make you feel more comfortable about it.

Maybe tell her that you have started questioning your own gender identity, and leave it at that for now. 
That way you can move in any direction once she has had time to take that in, and you can see her reaction.