An LCD gives a one or two line display for your Stamp.
The simplest, but most expensive solution is to purchase a serial interface LCD from Parallax. For example, the 2x16 LCD, Parallax part number 27910 costs $49.00. (November, 2004. If the web link is not active, search www.parallax.com for the part number). Parallax provides a manual that shows exactly how to interface with the Stamp using only a few i/o pins.
The low-cost solution is to purchase a plain LCD for $10 or less from a surplus electronics store and interface to the Stamp. This requires more pins and a bit more care in programming. An excellent application note is Note # 1 in the BASIC Stamp 1 Application Notes (If the web link is not active, go to the Downloads > Documentation section of www.parallax.com)