The web is a rich repository of information, and some important sites which we have used are :

www.usb.org - A good site for USB related data

www.rs485.org - A good site for or information regarding RS 485 standards, etc.

www. embedded.com - On-line magazine ( Embedded Systems Programming )

www.microcontroller.com - Good microcontroller sites.

www.chipdir.com - A very powerful mailing list is available on this site.
                            A lot of our problems were solved by using it.
                            A lot of other links are also available.

www.questlink.com - A good site to search for components

www.motioncontrol.com - A motion control site

www.ganssle.com - A very nice site with archive articles from
                             a guru of Embedded Systems, Jack Ganssle