Lots of ideas here http://racepaintusa.com/

 

My avatar is too small to really see but its a waving purple racing checkerboard pattern over stock color. the tank has a Harley Bar and Shield with flames eminating from the rear. Then it is all covered with a clear multi-color flake. I used Harley's flame collection to match the theme for the covers, grips, etc.

If flames are your thing then think about what some of your favorites things are and design the flames around that, ie; a Bulls head with flames surrounding it or maybe a flag with flames incorporated into it, etc, etc.

 

Here's a couple pictures of a previous project I had painted with flames.