Programming Languages at Mozilla.Org - This is the programming languages sub-tree of the "NewHoo" free directory project. The coverage is pretty broad, and sub-categorized quite well.

http://www.dmoz.org/Computers/Programming/Languages/

Free On-line Dictionary of Computing - Incredibly comprehensive alphabetical listing of computing terms, acronyms, phrases, and concepts. Nice search interface, but no links.

http://wombat.doc.ic.ac.uk/foldoc/index.html

ACM 'Hello World' Project - Very simple programs to print "Hello World". Several hundred languages covered, but sadly no links. Seems to have been quiescent since late 1997.

http://www.latech.edu/~acm/helloworld/HelloWorld.shtml

Ron Heuse's Coding History Pages - Alphabetical listing of about 2350 languages and language systems.

http://www.heuse.com/coding.htm

SAL - Languages and Compilers - Extensive listing of languages and compilers available for the Linux operating system.

http://sal.jyu.fi/F/1/

PC Webopedia Programming Languages category - Modest compendium of programming languages at a large commercial tech-encyclopedia site. Most of the entries have lots of links.

http://webopedia.internet.com/Programming/Programming_Languages/

Catalog of Free Compilers and Interpreters - Well-organized searchable database of programming language systems that are available for free.

http://www.idiom.com/free-compilers/

Yahoo! Programming Languages - Section of the Yahoo! topic tree for programming languages. Lots of good information; major languages have their own sub-sections. Unfortunately, it seems to have a lot of dead links.

http://d2.dir.ac2.yahoo.com/Computers_and_Internet/Programming_and_Development/

The U. of Michigan CIS400 Language Guide -Very nice collection of information about influential and popular programming languages. Many of the entries have code examples.

http://www.engin.umd.umich.edu/CIS/course.des/cis400/

Tunes Review of Programming Languages - As part of the TUNES project, F. Rideau is examining all existing languages, operating systems, virtual machines, and UI systems.

http://www.eleves.ens.fr:8080/home/rideau/Tunes/Review/Languages.html

Programming Language Preliminary Notes? - Helpful overviews of a few dozen languages, organized into neat little tables.

http://www.cs.colorado.edu/site/atoz/index.html

Brad Appleton's Programming Language Links - Big collection of links to programming language resources, including some for unusual languages and LOTS for popular languages. Simple and spare page design.

http://www.enteract.com/~bradapp/links/prog-langs.html