We've created a new tool on labs.realise.com. Just keep hitting the Everything button to generate random CSS gradients, which look a bit like mid-twentieth century wallpaper. If you find one you like, you can take the CSS (click on Get the CSS), and use it in your own site.
If you find one which is quite nice, but needs work, try randomising just the colour values, the variables or the pattern used. And if you want to go back to a wallpaper you generated a few clicks back, use the [<] button. Good design is just a matter of clicking buttons. If in doubt, click harder.
Each wallpaper has a unique ID - it's the bit after the # in the URL. If you share the URL, whoever follows it will see your unique wallpaper. There's those oh-so-2005 share buttons, to make this process slightly less painful, at the bottom of the page.
I created the Wallpaper Generator, after clicking about on the CSS3 Patterns Gallery, and wondering if a machine could generate something similar, using random numbers (spoilers: random numbers don't generate patterns quite as nice). Warning: some of the patterns are ... a little mammary in nature. Please address any complaints about these wallpaper to Mr. Richard F. Maths, the inventor of Mathematics.