So.....I don't know what to say here. These are incredibly nice photos and comparing them to the photo's of your nieces that you posted awhile back, I'm amazed at that improvement in less than 2 months.
Let me guess. You've been spending a lot of time doing 2 things. Strobist and practicing shooting? I think they all look great and I'll hit them 1 by 1 for you with my thoughts (humbled as can be by the way).
1. Great Lighting and beatiful against the perfectly exposed sky. Only slight problem to me is that I can look up her nose due to her pose versus your position. Not sure that you could have fixed that and had the same "feel" to the shot though.
2. You exposed her perfectly. My only problem is that her hair blends in the with the darkened interior of the car. It would have been cool if you could have thrown a strobe in the back seat to add a tiny bit of light to the interior (but still darker than the rest) and even a gelled strobe in there would have been cool maybe.
3. Pretty much the same thoughts as #2.
4. Very cool shots and love the exposure/lighting contrast between the subject and the background.
5. Again I like the contrast of the subject to background lighting.
Okay, I did my critique/opinion on them....now if you would be so kind to post the setup you used on these....I can tell where the lightsource came from, but was it hard light or umbrella? 1 and 2 seem like fairly soft light while the others are harder light.
I'm still amazed that in 2 months time I went from giving you a critique (on your neices photos) to wishing I could take photos like you (these). Great job man.
Almost forgot, but I really like your photoshopping techniques on these and I'd love to hear what you did on those.