On this most happy and important occasion, entertainment is a major component for success! In many cases, the very best choice is disc jockey entertainment. It's versatile, kids love it, and there is a broad range of options, from the popular basic service--which provides the DJ, the sound system and complete music library--to more elaborate DJ entertainment with all the bells and whistles!
If you prefer live entertainment, an exciting live band is a great idea. Bands of all descriptions are available, but probably the most popular for Bar and Bat Mitzvahs are Pop bands, Top-40 bands, Klezmer bands and Dance/Party bands.
For more elaborate and larger Bar and Bat Mitzvahs, consider using both a disc jockey and a live band. The DJ can play all the teens' favorite music, and make helpful announcements to get everyone participating in party activities. And for the adults, the band can provide swing and society dance music. Another impressive touch might be light background music for the cocktail and dinner portion of the evening, provided by a jazz combo, a classical group, or a soloist.
If you'd like to delight the younger children as well, an exciting and friendly novelty entertainer is very appropriate! Kids love to interact with these performers, and will talk for weeks about the fun they had at your Bar or Bat Mitzvah.