All Mixed Up Hangman
Good hangman word-guessing game for younger kids.

Animals
A really fun game where you think of an animal, then the computer asks questions until it guesses correctly.

Animals Guessing Game
Frames required for this game.

Cascoly Critters
Animal guessing game for downloading.

Fake Out
A word guessing game where, based on your grade or age, you pick a word and guess its meaning. Challenging.

Guess the Animal
Yet another animal guessing game, also very good.

Guess the Computer
This game is also know as Trial of the Nerds, from PBS.

Guess the Dictator
A game where the computer guesses who you are (dictator, despot, or TV character.) For older kids.

Java Hangman
Nice applet that lets you click on your letter choices rather than typing - plays very smoothly.

Mindspring Hangman
Hangman with big letters - good for younger kids.

Number Guess
An easy number-guessing game.

Pooh Guessing Game
Where is Pooh hiding?