Best on-line source for rolling stock photos?

[tmlbk]

I'm ready to start weathering and need prototype pictures but not engines at this point.

[Nelson]

http://www.railcarphotos.com  is one of the best

[3rdrail]

You did not specify era, so here are some both modern and historic:


http://www.rr-fallenflags.org/
http://www.nonotuck.us/kens/boxcars/index.html
http://prr.railfan.net/freight/
http://www.steamfreightcars.com/

[CoalPorter]

Northeast Railfan is great also.
http://www.northeast.railfan.net/

[The Donkey]

Can't forget http://www.rrpicturearchives.net/

[tom mann]

http://www.railcarphotos.com  is one of the best

I agree.  It's one of the easier to navigate, quickest loading sites for photos out there.  Plus, it's seems to feature photos from the Atlas gang, so if you make some assumptions, you can figure out what Atlas will release ahead of time

[cv_acr]

http://freight.railfan.ca

[tom mann]

http://freight.railfan.ca

...has a nice search function as well.