I don't have a problem with my daughter wearing any type or genre of clothing, style at all. I might personally not wear some of it, but I want her to figure her own style out and be herself. She happens to wear a really cool mix of different styles and her own set of "rules". Like, she is ok with a little pink, but not super girly. She likes flowers, but again, not if it's too little girlish. She layers different prints and colors, she MUST wear shorts under skirts and dresses, every time. lol (I've tried to get her to ease up on this a bit, especially if we are not going to be anywhere with a playground or something and we are running late and her shorts are not clean, but to no avail.) She's very distinctive, and this may just be what she would be like no matter what, but I'd like to think that a part of her "okayness" with being herself and claiming her own style is that I've let her figure it out without censure.
I will say that so far, she's been pretty immune to peer pressure with clothing. She has her criteria to meet, like comfort and her own taste and that is pretty much all she cares about. (She has, however, gotten a lot of flack from her father when she goes to his house and it just crushes her. He hates the way she dresses and makes arbitrary rules like no yoga pants to the grocery store. She worries about what clothes she wears there so he won't say anything bad to her)
My only rules have been making sure (and this is for all my kids) they have weather appropriate clothes, and nothing too darn revealing, and the clothing I buy needs to be well made. My guidelines on modesty might be a less strict than others though, I'm ok with two piece bathing suits, shorter shorts, etc.
Incidentally, I really hate all the Hannah Montana style clothing, I understand where you are coming from on that. But I try to bite my tongue and let her figure it out. I have always loved skulls though, and so does she. ;-)
(I'm also cracking up at her internally a lot right now, she's recently read a series about middle school aged vampires. the vamps in the town are called Goths and dress in black and stuff but are really harmless. She's now "into goth" and likes the cutesy skullys and stuff. "omg mom, isn't this so goth? " Snicker)
Sorry, one more thing. I grew up in a very conservative christian household. My mom had a similar way with me that I'm taking with my daughter and I was so thankful. She got a lot of flack from her friends and people in the church because I would wear all black with combat boots, but she always said "seriously? If I can let her have freedoms with as much as possible and this is the worst we deal with? I'm ok." . I went through a lot of fashion phases but never to rebel, because there wasn't anything to rebel against.