Its probably not widely know yet, but Martin Dobias (QGIS hacker who brought you many nice things including new symbology, python bindings, new labelling tool and the upcoming multi-threading renderer implementation) has been building up a very nice PyQGIS cookbook. The cookbook gives a very nice introduction into programming with the QGIS python api (it’s really easy, try it!). Other people have also been contributing to it and it would be great to get more examples, so if you have some nice tips / articles, checkout the cookbook sources here:
svn co http://svn.osgeo.org/qgis/docs/trunk/english_us/developer_cookbook
I’ve rendered out a PDF version of the PyQGIS Cookbook (click to download) in its current state, hopefully someone will find it useful.