The 'Steel Samurai' theme from the Phoenix Wright games. because I'm a fan of Gyakuten Saiben and Nick has a monotone 'Steel Samurai' ringtone also.
And my message tone? *fwoosh!* OBJECTION!
My brother has the MGS Codec for his ringtone, and even if he's out in public, he has to crouch behind something and say "This is Snake..." He's 24 and possibly the next nerdiest person after me.
He used to have a Left 4 Dead ringtone I composed for him.
Francis: "Hey, Louis! You look like shit!"
Louis: "Hey, man! That hurt!!"
Bill: "Don't be an ass, Francis!"
My sister has the 'Mail Bomb Strike' from WORMS as her message tone.
"Incoming!" *Fwoooosh...* "Nyeh-ehehehe!"