If you think it will be of use/interest to others, let me have the link and I'll put it on here.
If you don't find it below, try one of these links:
http://www.classic-car-directory.com/clubs/clublist.asp - also has postal addresses, contact names etc.
Country-specific sites:
www.american-auto-club.co.uk/ - American Auto Club UK
www.motorvatinusa.org.uk/ - American Vehicle Club
www.frenchcarforum.co.ukwww.italiancar.net/ - Italian cars general
www.berlinasportivo.com - Italian sport saloons
www.niimc.net - The Northern Ireland Italian Motor Club
Generic sites:
www.gsfcarparts.com/forum - Audi, VW, Saab, Volvo, Frenchies and Merc/BMW
www.hearseclub.co.uk - Hearses/limousines
http://retrorides.proboards.com - retro cars
www.pistonheads.comManufacturer-specific sites:
AC
www.cobraclub.comAlfa Romeo
www.aroc-uk.com - Alfa Romeo Owners Club
http://www.alfaowner.com http://forum.alfa156.net/ - Alfa 156
http://www.alfa155.org/forum - Alfa 155 enthusiasts including Q4 turbos
http://www.spyderchat.com - Spyder
Ariel Atom
http://www.arielmotor.co.uk/ Audi
www.club-audi.co.uk - Club Audi
http://www.audi-sport.net - Sporty Audis
www.rs246.com (R, S and RS model Audis)
www.audisrs.com (R, S and RS model Audis)
Austin-Morris
http://www.princessandambassador.org.ukhttp://www.austinmaxiclub.org http://www.morrismarina.org.ukBMW
http://forum.bmw5.co.uk/ - 5 series forum
http://www.bmwland.co.uk/talker/ - BMW forum (one of many)
http://www.x5world.com/forums.html - X5 forum (good for all BMW satnav FAQs)
http://www.zroadster.net - Z4 forum
http://www.e30zone.net - Early 3 Series include first M3s
http://www.thealpinaregister.com - BMW Alpinas
Citroen
www.cxoc.net - Citroen Xsara owners club
Daewoo
www.matizclub.com - Daewoo Matiz Owners Club
FIAT
www.bravo-guide.co.uk - Fiat Bravo Owners Club
www.sfconline.org.uk - Sporting Fiats Club
www.x1-9ownersclub.org.uk - Fiat X1/9 Owners Club
http://www.fiatforum.comhttp://www.puntosports.co.uk/ - Puntos
http://www.fiat.org.au - Fiat Australia Queensland
http://www.fiatclub.com.au - Fiat Australia New South Wales
http://www.fs-oc.net/ - Stilo
http://www.strada130.co.ukhttp://www.clubedomarea.com.br - FIAT Marea's Club
http://www.fiatclube.com.br - Fiat Club Brazil
http://www.fiatcoupeportugal.blogspot.com - Fiat Coupe Portugal
http://www.puntotd.com - Fiat Punto Portugal
http://www.clubcento.co.uk - FIAT Cinquecento, Seicento, 500 and Panda
http://www.forum.clubcento.co.uk - FIAT Cinquecento, Seicento, 500 and Panda
www.turbocollective.net - Uno Turbo / Italian turbocharged cars website
Ford
www.avoclub.com - AVO Owners Club Official Website
www.feoc-uk.com - Ford Escort Owners Club
www.fiestaclubgb.co.uk - Fiesta Club GB
www.ffoc.co.uk - Ford Focus Owners Club:
www.fordmondeoownersclub.co.uk/ - Ford Mondeo Owners Club
www.fpoc.co.uk - Ford Probe Owners Club
www.rs-ford.co.uk - RS Ford Owners Club
www.rsownersclub.co.uk - RS Ford Owners Club
www.transitvanclub.co.uk - Transit Van Club
www.passionford.comhttp://www.fordstownersclub.co.uk/ - ST owners Club
Honda
www.s2kuk.com - Honda S2000 Owners Club
Isuzu
www.itocuk.co.uk - Isuzu Trooper Owners Club
Jago
www.jagoownersclub.co.uk - Jago Owners club
Jaguar
http://www.jag-lovers.org/ - Jaguar
http://jaguardriver.co.uk/html/ - Jaguar
http://www.jec.org.uk - Jaguar Enthusiast Club
Lancia
http://www.lanciamotorclub.co.uk - Lancia Motor Club
http://www.stratossupersite.com - Lancia stratos club
LandRover
http://www.disco3.co.uk/forum/index.php - LandRover Disco3 Owners Club
Lotus
www.lotussevenclub.com - Caterham/Lotus Seven Club
http://www.lotusespritworld.com/www.seloc.orgMazda
www.mx5oc.co.uk - MX5 owners club
www.mazdarotaryclub.comhttp://www.323gtx.co.uk/Mercedes
www.baby-benz.com - Baby Benz Club (A Class Owners Club)
http://www.mbclub.co.uk/ - Merc club and forum, all models
http://www.mercedesforum.com/ - all models
http://www.slkworld.com - SLKs, R170, R171
Mini (Austin/BMW)
www.minicooper.org/index.html - mini cooper register
www.theminiforum.co.uk www.mini2.comMitsubishi
www.pajerouk.co.uk - Pajero Club UK
www.pocuk.com - Pajero Owners Club
www.mdocuk.com - Mitsubishi Delica Owners Club
www.lancerregister.comwww.lancer-evo.netwww.clubvr4.co.uk - For people with Mitsubishi Legnums or Galants.
www.lancerregister.com - Mitubishi Lancer owners club
www.coltuk.org - Mitsubishi Colt owners club
www.ftooc.org - FTO owners club
Nissan
www.purep10.co.uk/ - Nissan Primera Owners Club
www.nissan4x4ownersclub.co.uk - Nissan 4x4 Owners Club
www.sxoc.comwww.autosupplyuk.com/forums/index.php - Nissan Figaro owners club
www.gtiroc.com - Nissan GTi-R owners club
www.gtr.co.uk - Nissan Skyline GTR
www.skylineowners.com - Nissan Skyline
www.350z-uk.com - Nissan 350Z uk owners club/forum
Peugeot
www.psooc.com - Peugeot Sport Owners Club
http://www.306gti6.comhttp://www.106rallyeforum.com/forum2008/forum.phpReliant
http://www.reliantownersclub.co.uk/enter.htmlhttp://www.scimitarweb.com - Reliant Scimitar and Sabre Owners club
Renault
www.renaultforums.co.uk - Renault Owners Club
Clio Sport Renault Sport http://www.renaultalpineownersclub.com/ - Renault Alpine club
http://www.clubalpinerenault.org.uk/ - Alpine Renault club
Rover
http://www.the75andztclub.co.uk/ - Rover 75 and ZT
http://www.rovertech.nethttp://www.metropower.co.ukSkoda
www.briskoda.net - Skoda Owners Community
Subaru
http://www.scoobynet.comhttp://www.sidc.co.ukhttp://www.uklegacy.com/forums - Legacy forum
Toyota
Celica Clubwww.tlocuk.co.uk - Toyota Landcruiser Owners Club
Mr2 owners clubMr2 owners club2http://www.carina-e.com/main/news.php - Toyota Carina
http://www.supraforums.com - Toyota Supra
http://www.mkivsupra.net/TVR
www.tvr-car-club.co.uk Vauxhall
www.Astra-Sri.co.uk - Astra SRI Owners Club
www.mk3oc.com - Mk3 Astra
www.vauxhallownersnetwork.co.uk - Vauxhall Owners Network
www.Cavalierturbo.com - Vauxhall Cavalier turbo
www.migweb.co.uk - All Vauxhalls
Volkswagen
www.GolfGTI.co.uk - Golf GTI Owners Club
www.vr6oc.com - VW VR6 Owners Club
www.dormobile.org.uk - Dormobile Owners Club
http://www.vwgolfmk1.org.uk/ - VW Golf Mk1
http://uk-mkivs.net - MkIV Golfs
www.t4forum.co.ukVolvo
http://www.volvoforums.org.uk/ - Volvo
http://www.t5d5.org/ T5s, D5s and Rs
http://www.turbobricks.comGeneral Interesthttp://www.pocketgpsworld.com/modules.php?name=Forums - GPS speed camera updates