Here are three replacements you can make (either in the subject, message, or both):
%%input%%
%%condition%%
%%datetime%%
"condition" is the analog expression that caused the action to send a message.
"datetime" is the format of 2009-09-07 14:35:31 (GMT/UTC). I am working on re-writing the time with your timezone settings. Getting to work on all of the time zones plus day light savings adjustments has proved to be difficult. Once we get the local time zone adjusting the time, I will add it to the Wiki.