Simply Scripts - Movie Scripts Site - Best of the Net - Frequently Updated. Also has TV, Radio, Anime, Unproduced Scripts.
The Weekly Script - Downloadable movie scripts in text format. Updated weekly. Also has TV and Radio scripts.
Movie Page Movie Scripts - Movie Scripts Site - includes rare and unproduced scripts.
Daily Script - Movie Scripts Site - Blockbuster scripts. Frequently Updated. Also has TV scripts.

Script Sites - Genre

Sci Fi
Sci Fi and Fantasy Scripts - Movie Script Site - Science Fiction and Fantasy Movie Scripts
Leon's Script Collection - Movie Script Site - Quality Scripts - Classic Sci-Fi/Horror
Sci-Fi Movie Scripts - Links to Sci Fi movie scripts and transcripts.

Horror
HorrorLair.com - Movie Script Site - Horror and Suspense Movie Scripts
Cinefania - Movie Script Site - Horror and Suspense Movie Scripts

Horror World - Movie Script Site - Horror and Suspense Movie Scripts
Classic
Kingrr's Home Page - Movie Script Site - Quality Scripts - Classic Movies
Classic Movie Scripts - Movie Script and Transcript Site - not all in proper format - Classic Movies

Silent
Intertitle-o-rama - Database of intertitles from silent movies.
Photoplays - Database of screenplays, transcripts and translations of classic silent era films.

Script Sites - People

Affleck, Ben Ben and Matt - Scripts of Movies that Ben Affleck and Matt Damon have been in
Cage, Nicholas Cagefactor - Scripts of movies that Nicholas Cage has appeared in.
Cusack, John The John Cusack Fan Site - Scripts of Movies that John Cusack has been in
Cusack, John John Cusack Script Archive - Movie Script Site - Scripts of Movies that John Cusack has been in
Damon, Matt Ben and Matt - Scripts of Movies that Ben Affleck and Matt Damon have been in
Ford, Harrison Harrison Ford Web - Transcripts and scripts of movies that Harrison Ford has appeared in. In zip and text formats.
Kaufman, Charlie Being Charlie Kaufman - Scripts by Charlie Kaufman
McGregor, Ewan Ewan Reliquary - Scripts and Transcripts of movies in which Ewan McGregor has appeared
Northam, Jeremy Jeremy Northam's Lines - Transcripts and select lines of Movies that Jeremy Northam has appeared in.
Lewton, Val Val Lewton Screenplay Collection - Screenplays of films produced by Val Lewton, the 1940's B Horror Movie King
Scott, Ridley Ridley Scott Fan Information page - Movie Script Site - Scripts of Movies that Ridley Scott Has Directed

Hollywood Book City - Scripts for Sale
Planet MegaMalls - Scripts for Sale
Script Fly - Scripts for Sale
Scriptworld - Scripts for Sale

Script Sites - General

Awesome Movie Scripts - Movie Script Site - Large number of scripts, not all in proper format
Best Movie Scripts For Free - Movie Script Site - Infrequently Updated
Bradkoun's Home Page - Movie Script Site - Scripts in various formats - mostly action scripts
Colin's Movie Monologue Page - Movie Monologues from popular films
The Great American Screenplay - A selection of great American screenplays
INFlow's Screenplay Repository - Movie Script Site - Blockbuster scripts in proper format
iScriptdb Movie Screenplays Database - Movie Script Site - Infrequently Updated
JoBlo's Movie Scripts - Movie Script List Site
LeghornGMP - Alphabetized collection of scripts in text format. Not recently updated.
The Luna Lounge - Movie Script List Site
The Movie Script Compendium - Movie Script Site - Not Recently Updated
Movie Scripts - Links to movie scripts and transcripts.
A Movie Scripts Archive - Movie scripts and transcripts. Mixture of blockbuster and obscure movies.
Moviefreak - Movie Scripts - Movie Script List Site
Nemonic.Turf - Movie Script Site - Not Recently Updated
Only Good Movies - Movie Script List Site
Rosebud - scripts on the net - Movie Script Site - Infrequently Updated
Satan's Script-o-Rama - Movie Script Site - Not Recently Updated
ScriptCrawler - Links to movie scripts as well as tv, radio, and anime scripts. Searchable.
Screenplay 451 - Movie Script Site - Blockbuster scripts. Not Recently Updated
Screenplays For You - Blockbuster movie scripts. Script formatting good to very good. Locally hosted scripts. (Currently down)
Screenplays Online - Movie Script Site - Blockbuster scripts. Not Recently Updated
Scripts On The Net - Links to downloadable and purchase movie scripts. Searchable.
Scripts From Cult Classics - Movie Script Site - Blockbuster scripts. Not Recently Updated
Script-fix - Extensive alphabetical listing of on-line movie scripts.
Script-o-Rama - Alphabetical listing of downloadable movie scripts.
TwizTV Movie Scripts - Links to downloadable movie scripts and tv scripts and transcripts.
The Weekly Script - Downloadable movie scripts in text format. Updated weekly.
Write Movies - Searchable database of nothing but produced screenplays. No transcripts. Clean layout.