Bejewled

http://www.flash-games.org.uk/files/Bejeweled.php

Bejewled is a classic. The objective of this game is to swap one gem with an adjacent gem to form a horizontal or vertical chain of three or more gems. It is rumored to be the most addictive flash game ever. Fact is that it's one of the first widely acclaimed flash games and was released in 2001.

The game was a huge success for PopCap; more than 10 million copies of Bejeweled have been sold, and the game has been downloaded more than 150 million times.