Where can i find refrence photos?

Google and flickr ?

google image search using the "larger than..." filter is great. Youd be surprised at how many people upload full resolution images straight from their camera.

These might be helpful:

edit: Fail. Just realised you probably didn't want photos for inspiration... Haha ooops

CGTextures

http://www.cgtextures.com/

InterfaceLIFT

http://interfacelift.com/wallpaper/downloads/date/any/

Deviant Art

http://mjranum-stock.deviantart.com/gallery/

http://eteria-stockphoto.deviantart.com/gallery/

Personally I would have to say google, basically on the internet. Or if you can, take photos or something yourself for your own reference.

Internet is pretty good.. I'd start there. If that's too much, narrow it down to Google.

Seriously though, you didn't tell us what kind of stuff specifically. Do you need references for: guns, electronics, vehicles, furniture, people, creatures, architecture?

If you're looking for buildings, interiors or architecture, urban exploration forums are great for reference photos.

http://www.28dayslater.co.uk/forums/

I've found that one incredibly useful.

Reddit also has some awesome sub-reddits that are really specific and you can just subscribe to them.