An angle is given. Put the monkey on on the circle at the point that you think matches the angle. The closer your estimate, the more bananas you win! How many bananas can you win in 10 rounds?

http://www.oswego.org/ocsd-web/games/bananahunt/bhunt.html

Changing the Border
This is a nifty puzzle whose solution is based on the area of a triangle. The land is divided into two parts (P and Q) by the border ABC. Redraw a straight border line passing through point A so that each of the areas does not change.
http://www.ies.co.jp/math/java/geo/tochia/tochia.html

Dividing a Quadrilateral
This is a more challenging problem that is based on the same underlying concept.
http://www.ies.co.jp/math/java/geo/shi2to/shi2to.html

Clockwise
Either enter a time and see it displayed on the analogue clock, or click on 'Random' and type in the time shown on the clock. There are three difficulty levels.
http://www.shodor.org/interactivate/activities/ClockWise/

Elapsed Time
Practice finding elapsed time given a starting time and an ending time.
http://www.shodor.org/interactivate/activities/ElapsedTime/

Practice estimation skills by determining the number of objects, the length of a line, or the area of a shape. Choose the problem type, or choose 'Random' to see a mixture of all three types of estimation questions.

http://www.shodor.org/interactivate/activities/Estimator/

Type in your birth date (and time, if known), and this website will calculate your age to the nearest day (or hour, minute or second depending on how accurately you know your birth time).

http://www.mathcats.com/explore/age/calculator.html

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board?

http://www.interactivestuff.org/match/maker.phtml?featured=1&id=12

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board?

http://www.interactivestuff.org/match/maker.phtml?featured=1&id=27

Click on two cards to turn them over. If they match, they are cleared from the board. If not, they remain on the board. How many turns will it take you to clear the board?

http://www.interactivestuff.org/match/maker.phtml?featured=1&id=13

Type in a length and a unit, and this website will convert your boring old unit to something much more interesting, eg 200 cm converts to 39 AA batteries end to end, or 10 five month old human fetuses end to end or even 1.4 standard railway gauges. Fun and educational. Three thumbs up!

http://www.sensibleunits.com/

The students use the concept of triangulation to locate Digit.
http://pbskids.org/cyberchase/games/circles/