Blokus is fun strategy game that works very well for both kids and adults.  It is easy enough to learn that even my five year old son enjoys it.  There's also enough strategy to keep me interested.  Since winning is based on a score, it is easy to handicap the game and keep it challenging for everyone.

The only problem with the game is that with 2 players there isn't really enough competition for board space to keep the game interesting.  In fact, unless one player is very aggressive, 2 player games tend to end in a tie.  A simple way to fix this is to reduce the size of the board.  The normal game is played on a 20x20 board.  I have found that a 17x17 board tends to play about the same as a 20x20 with 3 players.  Typically one player will be able to use all of their tiles, but it is rare for both to do so.  A 16x16 board makes the game even more competitive for space.