There is no actual answer. Addressable leds (see above) is one approach, shift registers or port expanders (I2C/SPI) are another when your short on pins. Else your looking at e.g. a Mega where you can directly connect them. You need to take into account how much current the microcontroller (or shiftregister / port expander) can sink or source; for the micro on an Uno or Mega its 20mA per pin (safe limit), 100mA per port (8 pins) and 200mA total.
The approach also depends on if you need to be able to dim them or not; I don't think there is an Arduino board with 25 PWM outputs.