RS232 range
Black Box sells a variety of RS-232 extenders:
**broken link removed**
The ANSI/TIA/EIA/-232-F-1997 standard specifies a maximum cable capacitance, not a maximum length. In the appendix, it gives an example calculation with a particular cable capacitance, and arrives at 15 meters and 80 meters, but those apply only to the example cable.
However, many folks disregard the standard and use higher capacitance or higher data rates, and still have successful communication.