Hello I've been playing around with HTML&CSS recently and stumbled on quite a few websites with fancy backgrounds including one color smoothly changing into another from top to bottom, a wave dividing a page in two with one color above it and another below, backgrounds that look like sand-paper, buttons with crazy-shaped background etc etc you get the picture. While it's possible to create something like this in Microsoft Paint (by coloring single pixels all day!) or googling background images, I'm sure there there have to be some programs to create those simple (but complex by Microsoft Paint standars) graphics yourself. What program (or other solution) would you recommend?

Most can be done with CSS3 gradients and shapes and SVG too.
See :
http://www.colorzilla.com/gradient-editor/
http://css-tricks.com/examples/ShapesOfCSS/
http://sarasoueidan.com/blog/css-shapes/
http://www.html5code.nl/html5-canvas-tutorial-lines-shapes/
http://css-tricks.com/using-svg/

I don't suppose you need to colour each pixel in Paint to do that. Surely, it has some gradient tool and a pen tool to make vector lines.

BTW, can you post some URLs of those sites you saw?

I doubt it has that. It's like Notepad, has been basically the same through the years. But there are lots of graphic editors out there, many of them free.

thanks, I found GIMP to be just the job for me