Main link: http://www.automation.siemens.com/_en/portal/index.htm

Forum: http://www.automation.siemens.com/WW/forum/en/guests/Conference.aspx?ForumID=41

Catalog: http://www.automation.siemens.com/order_formular/html_00/resoform.asp?lang=en

Communities and forum

http://www.control.com/alist

http://www.edaboard.com/forums.html

http://www.plcs.net

http://www.mrplc.com

http://www.automatas.org/foro/index.php

http://www.infoplc.net/foro

http://www.plcforum.it/portale/index.php

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/

Ethernet & Co.

Ethernet protocol analyzer at http://www.wireshark.org/

Protocols description http://www.protocols.com

Contemporary Controls http://www.ccontrols.com/extension.htm

TCP/IP resources list http://www.private.org.il/tcpip_rl.html