Looking at 50 Cent's Candy Shop video, it is a clear example of the male gaze. It's a video that objectifies women and shows them as a tool for male use. Shown in this screen shot is the viewpoint of 50 Cent himself, looking at the woman being objectified in the video.
Moving on to Country Girl by Primal Scream, we see the female as a sexual character but not from the male perspective, and it shows her as a more in-control rebellious character, as shown in this screen shot.
In Madonna's Open Your Heart, we see her inviting people to look at her instead of being looked at unwillingly. We see this through the way she is dressed and the way she acts in the video. We also see her looking at the audience who - in this video - are the people looking right at her, so we see an example of the looking role being reversed.
Finally, in the video for Alejandro by Lady Gaga, we see the use of two new terms. The queer gaze and the pink pound. The queer gaze is as the name suggests, the idea of gay men looking at such a video. This is apparent as the men in the video are dressed as feminine, and the video shows Lady Gaga as the dominant character, almost being portrayed as a man. This is where the pink pound comes in. A term used to describe the general assumption that a man is earning a higher income than a woman, so a male gay couple with no children will be high earners that are able to spend their income on disposable goods. It seems that Lady Gaga is trying to tap into this market through this video. This picture shows her as a dominant character above a group of men.