The voice of the Catalyst at the end of the game is actually a combination of three voices: The boy that Shepard encounters in the first mission of the game, and the voices of the male and female Shepard, Mark Meer and Jennifer Hale.
The game's ending received such a negative reception that the development studio postponed all planned Downloadable Content to develop and release the free "Extended Cut" DLC, which expanded upon the original endings.
At one point in the game, Tali mentions that Shepard "sounds like a Vorcha." Mark Meer, who voices the male Shepard, also provides the voice for the Vorcha characters in the game.
In the DLC 'Citadel DLC' Ashley Williams and Commander Shepard have a drinking contest at the casino bar. At that moment a Vorcha and Batarian walk over to them. This is the conversation they have.
[The batarian hits Commander Shepard's arm to get his attention].
Batarian: "My friend doesn't like you Alliance types".
Ashley Williams: "Listen dude, we're trying to do something here".
[Commander Shepard focuses on the game again. The Batarian hits his arm once more].
Batarian: "I don't like you Alliance types either".
At this point Ashley and Shepard get annoyed and beat up the Vorcha and Batarian. This is a huge reference to Star Wars.
Kai Leng was modeled after actor/martial artist Joshua Shibata.