I have made this recommendation already last year but I will repeat because there are several new members and because the Game is currently on stock at amazon.com.
In 1995, German game inventor Klaus Teuber created the board game "Settlers of Catan" that caused turmoil in Germany: it won several prizes incl. "Game of the year". And millions (!) have been sold in the German speaking countries alone. There is a real Settlers-fever. There are several expansions of the Game in Germany. The Game and two expansions have been translated to English and are available at amazon.com.
The secret of the Game is that the rules are easy but the Game itself becomes complex. Each Game is different because the board changes each time. You have to built towns and cities on an island using the ressources you get. This sounds easy but is a great game. There are no aggressive elements.
Just take a look at: http://www.geocities.com/TimesSquare/Metro/5303/catan.html
Take a look at the reviews at amazon!
You can buy the board at
http://www.amazon.com/exec/obidos/tg/stores/detail/-/toys/B00001ZT4D/qid=1038163295/sr=2-1/ref=sr_2_1/002-0894207-1707223
You should start with the basic game but I recommend the Cities&Knights expansion (you need the basic game for the expansion):
http://www.amazon.com/exec/obidos/tg/stores/detail/-/toys/B00005LDWX/qid=1038163295/sr=2-3/ref=sr_2_3/002-0894207-1707223
There is also the Seafarers-expansion (everyone says C&K is better):
http://www.amazon.com/exec/obidos/tg/stores/detail/-/toys/B00001ZSSZ/qid=1038163295/sr=2-2/ref=sr_2_2/002-0894207-1707223
I just have to recommend this board Game that originated in Germany!