These aren’t particularly hard to web search for, but just in case you didn’t know they existed I figured I’d drop them here. I’ve used all three of these in the past and I think they do a good job of driving home how cool of patterns you can make in SVG with such little code.
Customizable SVG patterns and background designs for websites and blogs
A collection of repeatable SVG background patterns for you to use on your web projects.
SVG Patterns Gallery
SVG images are typically smaller than bitmap images and remain sharp on high-dpi screens. Unlike CSS3 gradients, SVG images are supported on IE9.
Original link is dead (conversation), and a temporary(?) version is up at this link.
Scalable Vector Graphics are crisp and clear and can be rendered in all modern browsers.
Totally awesome, well-stretched svg backgrounds, free for download.
You can customize them with things like colors and scale, which is a great touch: