If you are wanting to play with a bank of LEDs have a look at the TLC5947, it outputs 24 channels of constant current LED outputs. This RGB LED Circuit uses the TLC5947 and demonstrates how capable it is. If you want to have a look at the code for some ideas you can see the project page here.
“It uses one TLC5947 per 24 channels, which does 12-bit PWM on each individual channel. All the MCU has to do is shift in 12 bits per channel, and send a latch signal. The PWM clock signal is generated by the TLC5947′s, which makes it a lot easier to use than the TLC5940′s.”