For the breakdancing Yoda:
Go to the options screen on disc one, highlight the THX logo, enter “1138”. You can also view the clip here.
The Emperor performing standup before the Senate:
Press pause during the Emperor’s attack on Mace Windu, hit “666” on your remote.
A surfing Chewbacca:
During the scene where the Wookies go to battle, hit the pause button 4 times, and Chewie will be paddling on some bright blue waves with some purple and orange beach bunnies.
Anakin and Amidala (Padme) dirty talk:
During the scene with the two professing their love to each other, hit the subtitles button.
Here is an example of the text:
Anakin: I want you bad, baby.
Padme: You should have thought of that before you embraced evil incarnate.”
Anakin: But I thought chick dug bad boys?
If you have an XBox:
Stick disc two in and there is a two-level demo of the new Star Wars Battlefront II video game.