And then, if the impact is large enough, you have fun effects like mountain ranges changing, seas appearing, orbits decaying/widening, new orbital bodies... you can play merry hell with your world's physical characteristics.
DM: As you exit the forest of Arek-sulit you see the mountains of Eskade.
Player: Great! It will take us about a week to get to the Pass of Uris.
(One week, game time, later)
DM: The pass appears to have collapsed due to the recent meteor impact. You now face a 900 mile long mountain range stretching a quarter of the way across the continent.
Fun sounding, isn't it?
Of course, we are talking a phenomenally huge central body to have this kind of effect, but it would be something to think about. You could even, depending on the density of the meteor, have metals formed that are different than the meteor itself, or have new, super-hard crystals form around the area of impact. Possibilities are endless. Go to Comment
Arkths or Ravagers: These are large landbound crablike creatures about the size of Grizzly Bears. They live partially in the astreal plane. Their food is magic. They can sense it at huge distances. Since spells and such are hard to eat (being in motion) and magical places are the equivalent of a sea of krill to them, they are looking for magic stashed in concrete places. Their primary food source is magic items, alchemical potions, and enchantments. They do a pretty good job of mangling/ eating the physical aspect of said items in the process of chowing down. These things will be the bane of dungeons everywhere, as they will slowly eat away much of the treasure (and the magical traps... so it can be advantagous to follow these things). Note: They will attack people with highly magical natures (i.e. high magic powers). They will probably kill the person in the process of sucking out the power.