Dan writes an instructables about some interesting High Power Led driving circuits. He makes clear that driving a Led using a current source is way better that driving the LED using a constant voltage source. He also introduce us the pros and cons of usign a resistor to limit the current or using a DC-DC Switching regulator. The circuits he finaly presents are based on NFET and bipolar transistors and that’s a simple and cheap way to make a current source. Detailed information on how it works is presented.
A step by step guide to build your led current source - [Link]
Circuits for using High Power LED’s - [Link]