I'm constantly being asked by Actors at workshops if I have any material for them to practice working with. Here are a collection of links to all sorts of relevant and useful websites where you can find literally thousands of scripts.

http://www.pdfscreenplays.net/

@li-Tronics Scripts Page
Acting Scenes (for Kids 9-12)
Awesome Scripts & Screenplays
Cinefania
Drew's Scripts-O-Rama
Enter The Cinema
Fatty Boom Batty
Movie Centre

Manuskripten Arkiv
Inflow's Screenplay Repository
IScriptDB
Jo Blos's Movie Scripts
Movie Scripts Source
Movie-Page Scripts
Movie Script Compendium
Nemonic: Movie Turf
Only Good Movies
Play Collection
Quiet Harry's
Satan's Script-o-rama
Science Fiction & Fantasy Movie Scripts
ScreenPlay 451
Screenplays for You
Screenplay Listings @ About.com
Scriptcrawler
Scriptdude
Scripts on the Net
Script Shack
Simply Scripts
Splatter Nation (horror scripts)
Transcrips from Saturday Night Live
Zipped Scriptz