Since option is a character modifier usually, and for me at least produces useless characters in combination with j-k-l-i keys, the option key is a good modifier key.
Put the following in ~/Library/KeyBindings/DefaultKeyBinding.dict (create the file if it doesn't exist):
{
/* vi move left */
"~h" = "moveLeft:";
/* vi move down */
"~j" = "moveDown:";
/* vi move up */
"~k" = "moveUp:";
/* vi move right */
"~l" = "moveRight:";
}
Note that you have to relaunch the application before any changes take affect.
What key mappings do you guys use?
