HiTechnic have just released new NXT-G blocks that enable you to do simple Trigonometric functions such as sin, cos and atan2.
What would you need these for? Well when you're dealing with angles, you often need to calculate the length of the side of a triangle. Suppose your robot drives 1m forward, turns 23 degrees and then travels another 0.75m forward. How far are you from the start? That's where these blocks come in handy! I won't go into the math in this post but you get the idea. (wikipedia)
via - I'd rather be building robots