I just want to mention, that you should definitely check the pictures' licence models. pixabay has a lot of CC0, what is great. but my boss already got sued for using "royalty free pictures" on his site. so: read/check licences before using pictures - there are some lawyer agencies hunting for money, and they use automated bot search for that
For vector images, I use Vecteezy.
For uncopyrighted photos deviantART is definitely the best, but I've found something on Photobucket as well - since most users there are not companies or entities who care about copyright.