SidecarJohn

http://www.advrider.com/ - Not totally sidecar, but the Adventure Rider site has a very broad ranging Hacks (sidecars in USA speak) forum, which could be useful.

http://bmwmotorcycletech.info/EMLsidecar8.htm - Site for those owning, or intending to acquire an older model EML sidecar.

http://www.chairintheair.ca/ - Californian enthusiast's personal website.

http://www.endurosidecars.org.uk - "What it says on the tin."

http://www.hpsidecar.com/home/ - US high performance sidecars, includes a forum.

http://www.scooter-sidecars.com/ - Scooters and sidecars do go together.

http://www.sidecar.com - Site of the U.S.A. - United Sidecar Association, and the Sidecar Industry Council. now run by enthusiastic owners.

http://www.sidecar.it - Site of the Sidecar Museum in Cingoli, Italy.

http://www.sidecarmaniac.nl/ - Dutch high performance enthusiast's personal site

http://www.sidecar-cz.com - Interesting Czech site.

http://www.warkshop.com - This guy paints bikes, but there's a heavy emphasis on sidecars. Some good images.