The shortcut to switch tabs is…

TextMate:

Command + Option + Left/Right

Skype:

Command + Shift + Left/Right

Adium, Firefox:

Command + Left/Right

Colloquy, Firefox:

Command + Up/Down

Opera, Safari, Terminal:

Command + Shift + [/]

Dear Santa, please, bring me Mk 41 next christmas, so I can fix this world.