We are working with a red laser module < 3,5 mW from KEMO (Germany). Laser class 3A (TAKE CARE A LASER OF THIS CLASS IS ALREADY REALLY DANGEROUS AND MAY HARM YOU!). Wavelength approx. 670 nm. Operating voltage: 3V DC.
The typical current is about 80 mA.
We based our design on the one of Andreas PETER from Germany.
Three parallel resistors might seem strange, but this is our best solution for heat control, since a current of 80 mA through a resistor of 22R (which is the total resistance of the three), produces P = I2*R =145 mW, quite a lot ! Using three resistors, you have a better ratio heat to air-contact-surface. So, inside of the Lego-bricks, where the circuit will be placed, the heat is released more quickly to the environment.
Note that there is an important voltage dropdown at the RCX-connection. The capacitors help avoiding swinging effects. The Zener is placed as a security not to trepass the maximum voltage of 3V, which will definitely damage the laser module.