Someone already mentioned them, but anything by Yahtzee [http://www.fullyramblomatic.com/games.htm] is almost guaranteed to be good. Also, try The Way [http://www.crestfallen.us/], a series of free RPGs that should keep you going for a while.
Other decent freeware games I've encountered include Legend of Princess [http://www.konjak.org/], the Ben Jordan series [http://www.adventuregamestudio.co.uk/games.php?action=detail&id=760] and and the Merlin trilogy [http://www.adventuregamestudio.co.uk/games.php?action=detail&id=204].
Other decent freeware games I've encountered include Legend of Princess [http://www.konjak.org/], the Ben Jordan series [http://www.adventuregamestudio.co.uk/games.php?action=detail&id=760] and and the Merlin trilogy [http://www.adventuregamestudio.co.uk/games.php?action=detail&id=204].