One of my favorite websites for graphic design inspiration and tools is Creative Market. And a couple days ago they posted "60 Geometric Backgrounds" and they are BEAUTIFUL.this website.
You'll need Adobe Illsutrator CS5 and a web browser that supports API files (like Firefox or Chrome). So this is what ya gotta do:
1) Go to somestuff This will download a file, open "index.html", which will open in your web browser.
2) Create / find an image that you'd like to turn into the pattern. I used this one as an example:
3) Once the file has been uploaded, click the button on the top right "add 25 vertices: randomly"
5) Open Illustrator, and import the SVG file. Then open the "Align" box by going to Window -> Align. Then using the Direct Selection tool (shortcut key A), highlight the anchor points on the left and click the "Horizontal Align Left" box.