PSK31 is a great communications mode introduced by Peter Martinez (G3PLX) some time ago, that uses phase modulation and an optimized "Varicode" character coding. This allows for very narrow band, robust operation at reasonable speed avoiding the well-known "loss of sync" problem on one side, and the need to operate in a connection-oriented way (such as Pactor or Packet) on the other. It's about the same feeling as the old RTTY with much better overall performance. And it's very easy to set up thanks to the excellent soundcard DSP programs available.You really should give it a try !!! For more details see this article on PSK31 by G3PLX (pdf).
These are my 
favoured programs
PSK31SBW by G3PLX (very simple to start with PSK31)
DigiPan by KH6TY and UT2UZ (comfortable to operate PSK31)
Logger by Robert C. Furzer (very complete set of programs for PSK and station management)
WinPSKse by AE4JY and KA1DT (most comfortable, dual-channel PSK operation)
Click to play a PSK31 sound sample
PSK31SBW, the simple
one
and WinPSKse, comfort class 
73 .... Jürgen, DJ9ZL - [email protected],
Packet: [email protected]