The two Mass Effect games are awesome in their own right, but that's not the bit I'm suggesting.
As the player galavants around the galaxy map in both Mass Effect 1 and 2, various planets are encountered, all of which are given at least a short description. Said descriptions can be either lifted wholesale or easily adapted to fill in star systems when the Explorers start asking difficult questions like "what else is in the system?"
The mass effect wiki has a complete list here: javascript:void(0);/*1284647691655*/ (if that link works, this forum's got a weird format).
Examples, two as potential adventure sites (though not used as such in the game) and two as uninhabitable worlds there solely for flavour:
Etamis
is a superterrestrial world a third larger than Earth. It is in a "post-garden" state that clearly shows evidence of attack from space. While it's now waterless, the shores of former oceans show patterns of cratering too regular to be anything but saturation bombardment by dreadnought-class kinetic weapons, although it is unclear how most of the atmosphere has been lost. Archaeologists have found little of note. It appears that all settled regions were touched by the global bombardment. The few relics found suggest an advanced spacefaring culture thrived on the world from approximately 20 to 40 million years ago. The level of antiquity makes it impossible to estimate the world's former population or guess whether it was the race's homeworld or a colony.
A human-dominated world with over 95% of its surface covered by salt water,
Trident
is home to a dazzling array of life. The oceans are filled with creatures ranging from tiny bivalves to mammoth vertebrates unequaled even by Earth's whales and ichthyosaurs. Small archipelagos create what little land there is, and its valuable real estate is fought over constantly.
Underwater extraction operations have recovered a number of valuable minerals from the ocean floor, including iridium, uranium, and dust-form element zero. A largely lawless world, Trident is home to a rogues' gallery of unethical corporations exploiting the resources of the planet and actual rogues - criminals, slavers and mercenaries - working the shadows.
A small rock planet,
Makhaira
's thin atmosphere and high albedo keeps it from being much hotter than it is. The crust is high in sodium oxide, giving the planet a whitish tinge.
Home to 51 moons, including the prebiotic moon Anafiel,
Dumah
is a standard hydrogen-helium gas giant with violent surface winds exceeding 1,900 mph. Like its sister planet Elohi, it is believed to be an extrasolar capture.