About $250, but that was right during the huge drop in the stock market. Everyone was switching over to gold and advertisers were paying $1-5 per click for gold and silver related adsense. It was insane. Still going strong, but not as strong as those few weeks not too long ago.
mine's was $89 in a single day, but i think that's not my highest day yet because i already split the traffic to other site.
Mine was about $700 on one blog back around 2006, the blog went viral pretty much overnight because of an event I targeted at the time. From day 0 to day 1 it went from making nothing to about $50, after about 7 days it peaked at the $700 range, then over another 14 days it crashed to about $2-3 per day. After a year it was worth no more then a couple dollars a month. The event was the world cup, so I knew it would have crashed hard when I made it.