One of the most successful arcade of all times is Bubble Bobble.
Besides the awesome gameplay, one of its features that made it a successful game was its cute graphic design.
If you look at the picture, every level is made by a just a black screen with some platforms, but the patterns filling these platforms give the game an interesting look.
The following is a list of sites that offers patterns I think you can find useful for your next Flash arcade game.
Remember to check the license before using one of them for commercial use
www.brusheezy.com/patterns – free Photoshop patterns
squidfingers.com/patterns/1/ – more than 150 pixel patterns
www.dinpattern.com/index.php – some interesting big patterns that can be used as backgrounds
bgpatterns.com/ – online tool to create your own pattern
patterns.ava7.com/ – about one thousand patterns searchables by color and theme
www.deviantart.com/#catpath=resources/applications&order=9&q=pixel+pattern – more than 50 resources for pixel patterns
www.k10k.net/pixelpatterns/ – a lot of tiny pixel patterns
veredgf.fredfarm.com/pattern-bomb/ – patterns for non commercial use only
www.tilemachine.com/ – design your own tile or choose one from the gallery
http://www.kollermedia.at/pattern4u/ – more than 250 patterns
www.fontastica.com/pixel-patterns.html – pattern fonts, very “Game Boy” look
www.colourlovers.com/patterns – thousands of patterns
www.clickpopmedia.com/tag/pixel-patterns/ – some black/white pixel patterns
celestial-star.net/patterns/ – pattern files for Photoshop
www.stripegenerator.com/ – online tool to create your own striped pattern
If you know more, just let me know.