I primarily use MLCad, for both part authoring and model building, as I prefer its precision over quick LDD-style drag-and-drop.
I've put some time into creating new parts of Lutz Uhlmann's LGEO system, used for rendering LDraw models in POV-Ray, although I've submitted a few parts to the LDraw Parts Tracker with my relatively basic grasp of LDraw part creation.
On the LDraw.org wiki
As Willy has asked me to put together an updated LDraw to POV-Ray tutorial, I will be using a test page under my User page to start building it before publishing it as a "proper" page.
In Progress: POV-Ray Tutorial
It will take some information from the tutorial I wrote at Eurobricks, found here, although I plan on focusing more on getting good-looking radiosity.
LDraw colour comparison chart
This has been moved here.