Fun Strategy game for free online.

Here is a fun little game for anyone who likes strategy.

http://www.miniclip.com/games/canyon-defense-2/en/

Canyon Defense 2

There is more free games along this line such as

http://armorgames.com/play/10261/frontline-defense-2

If you are more simple minded there is always battleship..
http://www.learn4good.com/games/board/battleship.htm