lots of high resolution pictures to be found on a french site - www.tuning-auto.com under photos.
mostly individually tuned european cars, from car meetings etc, high quality good stuff, 10,000+ pictures so you have pleanty to chose from. a lot of cars are even too extreme with some really crazy bodykits and spoilers...
 forgot to mention that pictures are sorted according to car brands and according to meetings/shows as well. usually. e.g. if u click vw, then in the begining u get "regular" non-tuned stuff from big motorshows like geneva etc, so u have to move a couple of pages till you reach the good stuff
here are about 7-800 pictures (maybe even more) from car&model (which rencently has to be paid for)
anyway, the following link will provide you with thumbnails of very high resolution tuned car pictures.
be aware that it does take quite some time till the page loads completey, even though only thumbnails load, there are quite some of them
enjoy, and enter the monthly competitions, excuses like "couldnt find rims", "no nice body kit", "where do you guys get intercoolers from", "the perspective doesnt match", "i dont have high quality pics".... etc will not be accepted any more