1) Beyoncé's "If I Were A Boy" (embedding has been disabled by Youtube, so I only have a link)
The video for this song, off of Beyoncé's new album, features an incredibly serious and surprisingly subtle inversion of typically masculine and feminine stereotypes. It then surprisingly inverts them near the video's end in a way that could rightly be criticized as heavy-handed or obvious, though I would suspect that it's also a case of Beyoncé understanding that her intended audience might need more than a mere hint to get the point.
One of the reasons that this point - a statement on male privilege, where Beyoncé takes her boyfriend for granted, cheats on him, and laughs off his concerns - might need the explicit twist at the end is because the video's inversion doesn't totally work. Rather than becoming "a boy", her masculinized self has had masculinity grafted or added on to her femininity rather than replaced it. The inversion works for the most part during the exchanges with the boyfriend, but falls apart in public (her attractiveness is still coded in typically female ways - tight pants, hourglass figure) and in her interactions with other men, who stand above and behind her in conventionally familiar ways. One imagines that even the masculinized Beyoncé would not be immune to charges of being a whore, as little sense as that may make in the context of her song, because her "boy" character might be just as easily read as "ice queen" or simply "bitch".
All that said, this stuff probably constitutes the least important details of the video. Part of the lesson appears to be price of becoming like the boys - namely, the double-standard that exists when you fail to transition from the rules governing girls to a category of rules governing boys and are instead trapped inside both, subject to adhering to both at once. And the sudden transition to a stereotypical relationship between the two characters near the end also goes a ways to illustrating the tentativeness of women's masculine power, too - that is, even if you can hold a degree of masculine and feminine power at once, it's an anxious balance that's easily stripped away by those who wield more, and more secure, holds on that same privilege. And so the video fails because it's an exercise in realism.
2) Britney's "Womanizer" (again, embedding disabled)
But even if we found more to dislike than like in "If I Were A Boy"... well, thank god for Britney Spears, who lends some perspective by reminding us that while Beyoncé's video is flawed it could have been sooooo much worse.
Britney's various characters are also asserting some sort of power, a sort of campy masculine domination over an ostensible "womanizer" that's wronged them. But it's a wholly fantastical power, as the video's cheeky delivery undermines empowerment of these women in its joking presentation. This is the sort of thing that women might dream of doing, but it's not the sort of thing that any woman would actually do.
It's even sadder when we consider that the video's version of this woman's fantasy actually seems quite a bit more like a hegemonic man's fantasy. When the womanizer is being mobbed, we could be forgiven for wondering whether we should actually feel sorry for him - at times, it's not even entirely clear whether his punishment (?) is sex or... well, I'm not entirely sure what else it could be. Throw in the shots of a gratuitously nude Britney, with the womanizer seemingly showering in the background, and the audience can only be reasonably left with one conclusion: fantasy or not, being a womanizer is hot.