[Venture] from Hamilton, New Zealand offers a nice rear rack option that mounts to the four bungee mounts on the 1G Ninja. [Venture Cycles] is the distributor for the States. The rack kits consist of a pair of L-brackets and a Pack-Rack, Sport-Rack or a Grab-Handle. The racks aren't rated for much weight, but work great for storing gear when parked.
Do-It-Yourself
Some angled aluminum, sheet metal and hardware can be used to build one of these on the cheap. I used a cheap scooter top case for the first DIY kit.
Testimonials
sprale For my Ninja, I now have the Sport-Rack kit so I could mount a Givi 46L top case. The brackets also keep the saddlebags from rubbing against bodywork. The DIY worked well, but looked ugly. After getting rear-ended, the insurance paid for a replacement. :)