In Mass Effect 3 for the PC, PS3, and Xbox 360, you can recruit Tali’Zorah nar Rayya (aka Tali) to be a crew member on the Normandy.
You’ll be able to recruit Tali after doing missions on Rannoch. Once you destroy the Reaper on Rannoch, choose to side with the Quarian people and Tali should join you.
If you side with the Geth, Tali will commit suicide. The only way to keep her from doing this is if peace is reached between the Geth and the Quarian people.