Direct resistor voltage limiting is IMO a rather crude way of controlling LED brightness/power, as the resister has to handle the entire current of the LED (or more if you make the mistake of trying to do it parallel) When I was playing around with FPGA's a while ago I was able to use the FPGA as a PWM to nicely control LED brightness.
My analog parts kit has a 555 analog->digital timer IC in it, and I had heard you can make a PWM with it*, so that seems like a good second step in my journey.
(* - A cheap 8-pin microcontroller would also work. And be more fun.)
A good writeup is here: http://www.geocities.com/SiliconValley/2072/proj2.htm
I took this and tried to transcribe it into an Eagle schematic (lest this entry become completely unoriginal) I also made a board, although I'll never actually produce it so don't take it seriously. A microcontroller-board would be far better. ;)
For more information on schematic/board layouts, go here: http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=108 - the board layout stuff's the next tutorial.
Today was too busy so I don't actually have time to wire it up on the board. Or post pics of the very simple setup...