look for shift registers. The 74HC595 is very popular for Arduino:
The '595 is OK on the logic front but it still needs high-current drivers and resistors for every LED.
Have a look at one of the many functionally similar/equivalent shift registers like the TPIC6B595 (high-current but still needs one resistor per LED) or the TLC5916 (only needs a single resistor for each 16 LEDs).
There are also chips that can drive a heap of LEDs, the AS1130 for example can drive 132 of them and there's a thread here where someone has been using it and so presumably has some code.
EDIT: Found the thread
http://arduino.cc/forum/index.php/topic,122138.0.html
Rob