Here’s the formula to get the angle between two vectors in 2D space.

vector2 diff = target - position;
float angle = atan2(diff.y, diff.x);

A method to give materials a thickness property so light can shine through them. The thickness is saved as a alphachannel in which a higher value means thinner material (more light can shine through).

Link to the paper:
http://research.microsoft.com/~ppsloan/ldprt_final05.pdf

Most games that contains big cites doesn’t fill the buildings with proper interiors because of the cost in time and performace to do so. Instead they only apply a texture on the buildings exterior and make interiors only for a very few buildings that are of special interest for the player. With this method you can fake the interior of buildings without the need of much extra work from the artist, programmer or designer. The result can give very living cities.

Link to the paper describing the interior mapping in detail:
http://interiormapping.oogst3d.net/

 This method to do water is very mathematical but gives therefore a very realistic look. Specially the foam on the waves are great. The splash on the image appears if two waves hit each other.

Link to the article:
http://www.gamasutra.com/gdce/2001/jensen/jensen_01.htm

and this is the paper:

http://whitenight-games.chez-alice.fr/Docs/Water.pdf