Classic movies from 2010 to as far back as you can go.

Coraline is a solid all-ages movie. Slick stop-motion animation and it was adapted from one of Neil Gaiman's YA novellas.

Since you said you're into westerns, check out The Good, the Bad, and the Weird--it's a Korean western set in China in the 1930s, so that covers like three of your genres right there.

Note: Unless I mention "series" or numbers, I mean the original. I can't vouch for movies like Air Buddies 35, but Air Bud was GREAT.

All of the Disney movies
Ferngully
A League of Their Own
The Big Green
Little Rascals
The Sandlot
Air Bud
Casper
Angels in the Outfield
Cool Runnings
Little Giants
Honey! I Shrunk the Kids (series)
Don't Tell Mom the Babysitter's Dead
Adventures in Babysitting
3 Ninjas
Ghost
Dirty Dancing
Crybaby
The Outsiders
To Kill a Mockingbird
West Side Story

I could go on forever, but it's almost quittin' time. Best of luck!

Aside from the others you've already been given...
The last starfighter - That was one that I used to watch alot when I was a kid, and just recently saw again.
The Quick & the Dead

somewhat educational? I second the "Swing Kids" movie vote. Also Schindler's List, but that might be a bit too much for a 12 year old.