Not only is masturbation healthy and normal, it is beneficial psychologically, physically, and for your relationships!
Masturbation reduces stress, releases a "buildup" of stress, releases endorphins that make a person happier and have more energy, and it can even reduce the pain of menstrual cramps. Many other physical benefits have alreday been posted.
Masturbation is also practice for sexual intercourse in a relationship - when you masturbate, you understand which actions and which places bring you sexual pleasure, and then you can relay this information to your partner and the experience can be better for everyone; If you go in and have to leanr everything from scratch, it will take a few times for the experience to be as fun and pleasurable. Going in with no knowledge of how sexual pleasure works, and having high expectations of how wonderful the "first time" will be, can lead to a large let down.
Additionally, if you want to stay abstinate until marriage, what better way to stave off the desire for sexual intercourse by having sex with yourself instead? Masturbation has never gotten anyone pregnant, never given anyone an STD, and never made anyone go crazy.