Standard HD44780 LCDs are useful for creating standalone projects.
- 20 characters wide, 4 rows
- White text on blue background
- Connection port is 0.1" pitch, single row for easy breadboarding and wiring
- Single LED backlight with a resistor included, you can power it directly from 5V. If it's too bright for you, it can be dimmed easily with a resistor or PWM and uses much less power than LCD with EL (electroluminescent) backlights
- Can be fully controlled with only 6 digital lines!
- Built in character set supports English/Japanese text, see the HD44780 datasheet for the full character set
- Up to 8 extra characters can be created for custom glyphs or 'foreign' language support (like special accents)
- Comes with necessary contrast potentiometer and strip of header
For more information, check out Adafruit's detailed step-by-step Arduino+LCD tutorial
Adafruit have a generic 20x4 datasheet that has dimensions and pin-locations (the exact model may vary but the pinout, size and protocol information is the same). Adafruit also have a HD44780 datasheet with the detailed commands for control