12 Psychedelic Circles Patterns
These, free, retro, trippy circle patterns are vaguely reminiscent of 60s and 70s tie dye patterns. They work well at print resolutions, but will also scale down for the web. They are, of course, seamless and fully tileable.
If you're looking for similar retro wallpaper or background patterns, you might want to grab my Psychedelic Squares and Tie-Dye Style Patterns as well. Just click on my profile name.