dissections
There are lots of amazing dissections; I really like wooden ones; the picture below shows a nice wooden dissection puzzle available from educationinteractive. The pieces fit together to make a T. This is part of a range of similar puzzles.
I gave this to my year 8 students to have a go at (see video on the right). The solution to this puzzle is here if you are interested. 

dissection investigations
This would be a good way to investigate area (and perimeter) with students.
For example, you could present the very simple dissection problem on the right (click to enlarge). An extension to this might be how to dissect this triangle into a square. It is actually possible to create any other polygon from any other polygon, but the interesting thing lies in doing it in as few cuts as possible. So you could extend this to different shapes such as trapeziums, rhombuses and kites; I think this would be a good way of exploring the area and characteristics of 2D shapes. Below are some more dissection tasks from SMILE (click to enlarge): 



