I let my kids associate with other kids whose behavior I don't always like, and whose parents don't parent exactly the way I do. Sometimes this is because said parents are my friends. Examples: my best childhood friend, an athiest, is letting her DH raise their daughters in his church; as a result, they are very expressive of their religion, which is distinctly different from ours. Another example: a friend in the SCA who spanks (well, the dad does, the mom's not so thrilled about that form of discipline), and whose house I haven't been able to let DD go to because it's such a mess (like, borderline wondering if my friend is a hoarder or has other serious prob messy, with nasty roach infestation). Their kids are also heavily steeped in TV pop culture, manifesting by turns a Power Rangers and then a Bakugan obsession; I've tried to limit the media influence on DD's toys a bit more. I babysit the SCA friend's kids regularly, and they all play great together. I'm considering letting DD go visit at their house after they've moved, since they seem to be leaving the mess behind.
The neighborhood kids I have a bigger problem with; DD wants to go out and play with them, so I let her try, but the families closest to us have a combination of girls a few years older, and boys close to her age. The girls don't want to play with her much because they think she's too young, and will walk her home saying they have to go inside, then keep playing outside, which hurts DD's feelings (partly because she doesn't need to be walked home, and partly because they're clearly still playing). And the boys usually just don't want to play with her because she's a girl and physically smaller than them.
The kids in her homeschool enrichment group last year left me less than thrilled; at the end of the year, DD took the class picture while I was sleeping and scribbled out all the boys' pictures and circled the girls. I know part of this has to do with age-typical gender association, but part is also due to the teasing they did over her short haircut last year, of kids saying she looked like a boy. The irony there is that she herself still tries to categorize kids as boy/girl based on short/long hair. She wanted to dye her hair blue a few weeks ago, but wasn't entirely sure about it because she was afraid people would think she was a boy. I assured her it would wash out before Eagleridge started up in the fall (she knew SCA friend kids wouldn't tease her; her friend Thomas, for all that he's boy-pop-culture obsessed, usually dresses up in her pink princess dress when he comes over, lol), and I think it helped that when my sister came to get her last week to take her back to Texas for a visit, she had blue streaks in her hair.
To make a long story short, I do endeavor to ensure that adult family are DD's main role models, seconded by her 13 and 11 yo. stepbrothers (who for all that their mom lets them watch horror movies and the one is a bit too video-game obssessed for my taste, are young gentlemen and good role models for behavior and manners) and that her most-seen peers are friends' kids who, though their families may do things differently, are generally at least as well-behaved as DD.