1) Divorced couple, both scientists, highly antagonistic towards each other until said disaster forces reconciliation.
2) Spunky kid who nobody understands but who plays huge role in averting disaster.
3) Old man in flanelette shirt (usually the dad of one member of the divorced couple) who is wise but misunderstood and whose warnings are ignored.
4) Extremely thick law enforcement officials who care for their positions more than the impending destruction of the world.
5) A dog. The dog is there for cuteness value, but could also do one of i) alerting good guys to hiding bad guys ii) barking an important warning iii) pissing on highly important piece of evil electronic equipment.
1Yes, if you can't tell already, I've just watched yet another of these. This one had the Moon about to crash into Earth. It even had a choice line where the President of the United States asks if anyone will survive the collision.