Whenever I do a project on Photoshop or GIMP there are always a few things I need to complete it or start it. Whether it's a signature or a youtube background here are some sites that can provide pre-rendered images, brushes,fonts and other things such as textures and stock backgrounds etc.
This doesn't require registration but registration can be useful to give feedback on downloaded items and upload pictures or artwork.
I get most of my textures,brushes, stocks and fractal/c4ds from this website. It's a very useful place!
There are some renders here but alot of pictures are drawings,paintings or digital art.
This place is awesome for renders and fractals. You need to register before you can download them, but all images have a transparent background and there are thousands of images to choose from. This is more for video games, cartoons, gamer renders.
This is a good website for stock images. It is linked to another premium stock website called iStock which do provide better quality stocks for a price. This website does have very good stock images but also requires registration. This is not like planetrenders though, pictures provided here are real life photography of people,scenery and objects.
Usually if you know what font you want you can just type it into google and voila.
These websites are free, no registration required and provide thousands of fonts to browse through and download. Great for every kind of signature or design when lacking a suitable style of text. I'm always stuck for suitable fonts and find myself coming bac and checking for that perfect style of writing!