Really Good Simulations (includes Linear Programming!)
http://teacherlink.org/content/math/interactive/flash/

Theorem of the Day  
http://www.theoremoftheday.org/

Scarecrow_sh.mp4

Interactive Maths
http://interactivemaths.net/

Various Applets: http://illuminations.nctm.org/Activities.aspx?grade=4

Logic Puzzles: http://www.truthtree.com/mathdoor.html

More Applets from Wolfram: http://demonstrations.wolfram.com    
Download the viewer to see these.

Geogebra Applets
http://mathplotter.lawrenceville.org/mathplotter/mathPage/index.htm

ScribLink (online whiteboard)
http://www.scriblink.com/

Whats in a name?
HTTP://www.babynamewizard.com/namevoyager/lnv0105.html

Wordle
http://wordle.net/