Most Helpful Girl
Although I usually find texting much less intimidating, face to face is definitely the way to do it.
I think that the best way to do it is towards the middle/end of a casual date, when you're both feeling relaxed and stress free, and then find a way to say "so what are we right now?". When I did this with my boyfriend, I think the conversation went a bit like this :
Us - both talking and laughing normally
Me -*stares in that 'i like you're way*
Him - what?
Me - I just really like you, you know?
Him - I like you too lex (my name)
Me- I just... What are we? I mean, are we just friends, or something more, or what should I introduce you as if we bump into someone I know?
Him - what would you like us to be?
Me - that depends... What would you like us to be?
Him - I'd like to call you my girlfriend... if that's okay?
Me - *blushing furiously at this point* umm, yeah, I'd like that. I'd really like that. So we're together then? As in dating?
Him - I think so
Me - cool
And that was that!