If you mouse over the planet exploration percentage in the bottom panel of the HUD, it will give a short description of what each planetary bonus does, which usually makes sense with the bonus involved.

In any case, the names are usually self-explanatory: Habitable Cavern Systems provide additional living space (+population) and it is underground (+planet HP), Weapons Test Facility occupies space otherwise usable for living space (-population) and increases the defensibility of the gravity well (+tactical slots), Mega Fauna reduces available living space (-population) but the pelts and such from these animals are an exportable good (+trade income), Ionic Storms are dangerous to any planet-side population (-population) but are also a source of exportable energy (+trade income). Vanilla Sins has 21 planetary bonuses, Entrenchment adds a few more.

The only planetary bonus without any actual gameplay effect would be the Space Ponies, which (afaik) is some sort of an inside joke among the Sins beta testers, and this bonus is found entirely at random.

If you find it, mouse over it in the Artifacts tab in the Research window. I can't remember the description off the top of my head, but it has something to do with managing and optimizing the administration of the populace of your planets, leading to increased tax income and population growth rate.