General Background

The British Library:

"Language and the written word" page illustrating scripts from different period documents -- Beowulf to Virginia Woolf.
http://www.bl.uk/learning/langlit/changlang/writtenword/writtenwordtimeline.html

"Make a book" - Use this website to research and make your own unique artist's notebook, inspired by the Lindisfarne Gospels.
http://www.bl.uk/learning/artimages/sacredbook/sacredbook.html

"Why write?" - These pages will allow you to explore how writing can incorporate sight, sound, touch and gesture. You will also see the ways in which cultural, social, historical and personal circumstances influence the way we write and the scripts we create.

AncientScripts.com by Lawrence K Lo is a great site for getting an overview of writing systems and their history. 
http://www.ancientscripts.com/ 

Alphapage. An animated view of the evolution of alphabets. (This page is part of the course material for "History of the Alphabets" taught by Prof. RobertFradkin at University of Maryland.) 
http://www.wam.umd.edu/~rfradkin/alphapage.html 

Odyssey Online Museum outreach project at Emory University has a simple description, illustrations and games for writing systems in the ancient world: Near East; Greece; Rome; (The Rome entry includes a page on the Roman contribution of the codex to book making (vs. the scroll). 
http://carlos.emory.edu/ODYSSEY/MidElem_Home.html 

Cornell University:  Paper, Leather, Clay and Stone - the Written Word Materialized
Museum exhibit with educator resources.
http://rmc.library.cornell.edu/Paper-exhibit/default.html

Arabic

Sakkal Design: Art of Arabic Calligraphy 
A well-written site on Arabic Calligraphy by Mamoun Sakkal. 
http://www.sakkal.com/Arab_Calligraphy_Art4.html

http://www.shariahprogram.ca/Arabic-alphabet14.shtml
A detailed site with audio files and lessons on reading Arabic from The Toronto Shariah Program

Cuneiform

Cuneiform Digital Library Initiative (a joint project of the University of California at Los Angeles and the Max Planck Institute for the Hisotry of Science) has extensive images and educational background on cuneiform.
http://cdli.ucla.edu/

University of Pennsylvania's Write like a Babylonian game translates your monogram into cuneiform.
http://www.penn.museum/cgi/cuneiform.cgi

British Museum's student's site on writing in MesopotamiaAs you might expect, the British Museum has a well-annotated classroom site on the history or cuneiform with lots of images from their collection. 

Chinese Writing

China the Beautiful is one of my favorite sites on the Web for Chinese calligraphy. They also have a great page on printing. 
http://chinapage.com/china.html 

U. C. Berkeley collection of rubbings offers visual examples of calligraphy 
http://sunsite.berkeley.edu/Rubbings/ 

Cyrillic

Medieval Writing: History, Heritage and Data Source by Dr Dianne Tillotson is a friendly resource for Western European medieval handwriting as well as background on the Roman era. I advise going to the site map and checking out the various scripts and exercises. In the exercises Dr. Tillotson uses interactive demonstrations to identify familiar letters in different historic hands. 
http://medievalwriting.50megs.com/writing.htm

There are a lot of good sites for manuscript images available on-line. One place to start is the British Museum. 
Gutenberg Bible The British Museum has posted extensive images of this famous 15th century example of the introduction  printed Latin script. The BM has also posted good web sites for other "treasure" manuscripts in their possession such as Beowulf, the Lindisfarne Gospels and the Magna Carta. 
http://prodigi.bl.uk/gutenbg/ 

Sanskrit

Sanskrit Letters and Numbers from UK India Sanskrit lesson site at http://www.ukindia.com/zip/zsan01.htm

Languages and Scripts of India is a useful reference site for links to historical development and images.
http://www.cs.colostate.edu/~malaiya/scripts.html