xPL Project
Official xPL Project site. Contains the xPL specification documents and major downloads.

xPL Forums
Forums dedicated to xPL. This is the place to go for technical support.

xPL4Java
xPL4Java and xPL4Linux frameworks, as well as xPL control of UPB (Universal Power Bus) devices.

Tom Van den Panhuyzen's site
Tom is one of the developers of the .NET xPL library. His site is also home to the xPL Medusa CM11 service for X10 control.

xPL Perl
Mark Hindess is creating a Perl API for xPL.

Frank McAlinden's HA site
Various HA hardware projects - including the FirM zoned infra-red messenger - plus an xPL section.

Gadget Shed
Steve Cooper's site contains many useful xPL applications and VB scripts.