Just gonna say it flat out: Taking other kinds of dance besides ballet is EXTREMELY important, and often the factors of getting accepted into a company hinge upon that. Being skilled or having training in other types of dance such as hula, hip-hop, contemporary, Bollywood, and musical theater greatly increases your success and versatility. I am currently taking contemporary and it has DEFINITELY helped me in ballet with expressionism and technique.
Contemporary is very similar to ballet, loose and flowy with precise lines. The individual movements are more modern than classical ballet, many of them are made up on the spot by the choreographer. Unlike ballet, contemporary is easily translated into different moods, happy, sad, in love, dead, alive, hurt, angry, alien, etc.
Hip-Hop is another form of expressionism. You can show you're hurt, in love, angry, etc. I personally find this form of dancing more fun to do and more entertaining to watch than contemporary. Hip-hop can consist of bboying, breaking, and also krumping has spurred from hip-hop movements.
Bollywood dance is the classic dance of Indian culture. It can be used to songs from that culture, as the dance above, or to popular songs of today, combining cultures in an intriguing mashup of dances. This dancing build muscle and is very difficult, but provokes a happier being.
Hula dancing is a different dance than most, and not many people outside of Hawaiian culture take it. I LOVE hula dancing and it builds control over separated part of the body, keeping still the top half of your body, while moving the bottom half. Isolation is key in ballet.
There are hundreds of styles of dance, and every one of them can help you in your dance training in becoming more versatile and strong.