My WonderSystems addon for the systemtypes.txt
There is a planetary system colliding with a storm, which provides lots of cloaked planets, dangerous energy fields, and various other effects around the planets. A great stronghold position where attackers will have to bring in many specialized ship designs.
A nomadic planet & moon system. A nice, dense package of territory, but no star means resupply may be a problem.
A unique planetary system with lots of dual planets. These are just cool to have. Romulans might like to start here.