Every time "quiz kid" Donnie Smith is in his car, the song "Dreams" by Gabrielle is playing. It is also playing in the police officer's car at the end.

During the beginning of the movie, and a little in to it, the number "82" appears 6 or more times, in various places (tattoo on guy being hanged, time is 8:20, etc.)  If you consult a bible, you will see that in Chapter 8, verse 2, in the book of Exodus, the passage talks about the appearance of frogs when Aaron holds out his hand.

In every living room there is a picture of a Magnolia.