Off the top of my head I can list a few.
/votemute - Opens a menu to votemute a player (restricts voice chat). Basically guardbanning on JB. Could also be used as
/votemute [name].
/votegag - Opens a menu to votegag a player (restricts text chat). Could also be used as
/votegag [name].
/votesilence - Opens a menu to votesilence a player (gag + mute). Could also be used as
/votesilence [name].
/votekick - Opens a menu to votekick a player. Could also be used as
/votekick [name].
/voteslay - Opens a menu to voteslay a player. Could also be used as
/voteslay [name].
/colorme [valid colour] - Allows you to colour yourself a certain body cosmetics a certain colour.
/mypitch [24 - 255] - Allows you to increase or decrease your voice command pitch. Also affects the Announcer's voice lines.
/voicefx (removed from JB only I believe) - Allows you to tamper with your voice effects with certain filters.
/ccc - Allows you to change the colour of your tag, name and chat colour freely.
/robot - Turns you into a robot. Can be abused by going Heavy w/ Stock Fists/reskin of Stock Fists to taunt kill, as no animation is shown