Show text in large type on the screen via terminal
Since you already have QuickSilver installed:

osascript -e 'tell application "Quicksilver" to show large type "your text here"'


You can use this to define a bash function (and put somewhere like ~/.profile):

function big {
        osascript -e "tell application \"Quicksilver\" to show large type \"$1\""
}


Then you can invoke it with arbitrary strings by doing

$ big "This will cause large text to appear"