One more radiant link. Found it looking in google for a broken link in dONKEY's site. It contains a ton of things neatly organized and explained rather than some long tutorials encompassing the creation of a whole level. This has the advantage that you only have to look for the particular thing you want to do instead of diving through the chapters of a guide.
Particularly useful can be the last section, "Qworkshop tuts", as it is even easier to find what you need there.