Tutorials and self-teaching resources
Tutorials at Siemens http://www.automation.siemens.com/fea/html_76/down_module.htm Tutorials at ENM http://www.enm.com/training/siemensstepcourses.asp#Basics%20of%20PLCs
Tutorials by Hugh Jack http://claymore.engineer.gvsu.edu/~jackh/plcbook.html
Tutorials and training stuff at industrialtext http://www.industrialtext.com/
Tutorials at the learning pit http://www.thelearningpit.com/
Tutorials at plcman http://www.plcman.co.uk/plc/
The Automation List PLC files archive: http://www.control.com/PLCArchive
Best Friend Tutorials: http://www.infoplc.net/