Unlock master difficulty
To unlock master difficulty simply do the following:

Master difficulty for Obi-wan - beat Anakin on any difficulty
Master difficulty for Anakin - beat Obi on any difficuly

Unlocking Star Fighters in Multiplayer
In Multiplayer mode, you can unlock several starships by beating the character AI based on characters related to the ships (ie - Luke and the X-Wing) in combat.

X-Wing - Beat the Luke Bot
Millenium Falcon - Beat the Solo Bot
General Grevious's Starfighter - Beat General Grevious Bot
Anakin's Starfighter - Beat the Anakin Bot
Darth Vader's Tie Fighter - Defeat Darth Vader Bot
Slave I - Defeat Fett Bot