Just Cows
http://www.arrakis.es/~eledu/justcows.htm
Cow in 539 languages. Misnamed Esperanto as an artificial language, but it does give you a clearer sense of the breadth of world languages. It's also a portal to language reference sites.

A Collection of Word Oddities and Trivia
http://members.aol.com/gulfhigh2/words1.html
An indespensible omnibus for word geeks!

Alt Key Codes
http://tlt.its.psu.edu/suggestions/international/accents/codealt.html
Great Reference page for the alt codes for all sorts of special characters.

Oðblgshezi: Calculator Words
http://www.langmaker.com/calculatorwords.htm
I don't know about you, but this stuff was fascinating when I was 10 years old.

Omniglot: a guide to written language
http://www.omniglot.com
Good place to see different alphabets

The Greeking Machine
http://www.duckisland.com/GreekMachine.asp
Great way to get some dummy text is you're laying something out pre-content

What does the filler text "lorem ipsum" mean?
http://www.straightdope.com/columns/010216.html
The Straight Dope on Greeking

Welcomes from around the world
http://www.visualwriter.com/Welcome.htm

Translation sites
Some languages not commonly taught in high school, oh, wait...

The Dialectizer
http://rinkworks.com/dialect/
Translate any webpage or text into Redneck, Jive, Cockney, Elmer Fudd, Swedish Chef, Moron, Pig Latin, or Hacker.

The Drug Slang Translator
http://www.brunching.com/toys/drugslanger.html
Tip of the iceberg compared to this.

Lame
http://www.ibiblio.org/dbarberi/lame/
use th1Z site To l0ok m0R3 creDiB|3 1N CHat r0omZ.

Pornolize
http://www.pornolize.com/
Gets me kinda hot...

Spam Mimic
http://www.spammimic.com/
Hide a secret message in their spam email, like a needle in a haystack.

more translators

Dialects

International Dialects of English Archive
http://www.ku.edu/~idea/northamerica/usa/wisconsin/wisconsin.htm
A fantastic resource to hear voices and dialects from all over the world. But where's Minnesota, eh?

Dialect Survey from Harvard University
http://cfprod01.imt.uwm.edu/Dept/FLL/linguistics/dialect/
122 maps of regional variations on terms and pronounciation. This is where I found out that a Gaper's Block was darn specific to Chicago, and so foreign to me when I moved from Minnesota. Which makes it's such a darn clever name for a chicago blog.

Accents by Kevin Kling http://www.npr.org/ramfiles/atc/20000704.atc.08.rmm
This Independence Day segment from All Things Considered is a brilliant synopsis of American dialects. Kevin Kling is a Minnesotan writer and playwright, thus his accent. He's a Kevin Kling fan page with links to other stories.