Typing a race series into Google/Photos will get you great results. Also Flickr searches work great, just type in a race series or car
European Race Leagues - http://www.automobilsport.com/
Race Shots - http://www.raceshots.be/index.php?page=home&lang=english
Racing Sports Cars - http://www.raceshots.be/index.php?page=home&lang=english
Planet Lemans (High Quality Fia GT and 24hr pics) - http://www.planetlemans.com/gallery/
Japenese Sports Cars - http://www.japanesesportcars.com/galleries/
Various European Touring Car Pics - http://www.flickr.com/photos/ride_industries/collections/72157600047446149/
Speed Pictures - http://server.selltec.com/go/speedpictures/
Misc. Japanese Time Attack - http://flickr.com/photos/auto-otaku/sets/
Misc. V8 Supercars & Australian Touring Cars - http://www.flickr.com/photos/davesmithmotorsport/
Blog with alot of cool RX 7's - http://rextreme.blogspot.com/2006/01/welcome.html
Tons of BMW Diecast - http://www.bimmer.jp/RaceC1.htm
Here's links for some of the racing leagues around the world. All have galleries listed under Gallery or Multimedia
American Le Mans - http://www.americanlemans.com/home/ALMSHome.aspx
SCCA World Challenge - http://www.world-challenge.com/index.php
Koni Challenge - http://grand-am.com/koni/
Rolex Sports Car Series - http://grand-am.com/rolex/
WTCC - http://www.fiawtcc.com/
BTCC - http://www.btcc-racing.com/
More BTCC - http://www.btcseries.be/nl/
VW Fun Cup - http://www.vwfuncup.be/nl/foto-video-galerij/
Japans Super GT - http://supergt.net/en/
SuperGT Race Archive (Pics from every race) - http://supergt.net/supergt/history/indexen.htm
2007 Super GT Teams - http://supergt.net/supergt/2007/07team/index_en.htm
2004 Super GT Teams - http://supergt.net/jgtc/race/2004/04team/04team_idx_en.htm
2005 Super GT Teams - http://supergt.net/supergt/2005/05team/index_en.htm
2006 Super GT Teams - http://supergt.net/supergt/2006/06team/index_en.htm
Asian Touring Car - http://www.afos.com/index.php
07' Super Taikyu - http://www.so-net.ne.jp/car/s-taikyu/2007/gallery/index.html#sgcar
FIA GT - http://www.fiagt.com/index.php
British GT - http://www.britishgt.com/gallery.php
Spanish GT - http://gtsport.es/default.asp
Nordic Supercar - http://www.nordicsupercar.com/galleri.php
BFGoodrich Long Distance Championship - http://www.vln.de/rennen.php
2006 Zurich 24 Hour - http://adac.24h-rennen.de/en/archive/2006/multimedia/pictures.html
2005 Zurich 24 Hour - http://adac.24h-rennen.de/en/archive/2005/pictures.html