Play Board Games posts an updated 2011 list of the Top Ten Gateway Board Games.
From their website:
Let me define gateway games. A gateway game has to appeal to people that do not play designer (or Euro) board games regularly, cannot be too complex and should introduce some new mechanics common to designer board games. As a caveat I am only listing games I have played. Some other gateway games that I have not played but heard are fun have been listed with my Honorable Mentions.