Sum - Simple Maths Puzzle - How fast can you add two numbers?
NumberDrop - A uniquely challenging math puzzle game.
dworksheets.com - Free K-12 math worksheets to assist students, teachers, parents & tutors to practice, teach or prepare grade school assignments, classwork or homework questions & answers is available online in printable & downloadable format.
Griddition - Griddition is a challenging numbers puzzle where you must fill a grid with numbers, Sudoku-style.
Seqitaire - Seqitaire is a free arithmetic puzzle game that incorporates gameplay elements of Solitaire and other classic card games.
HoDoKu - HoDoKu is a sudoku helper written in Java and available in English and German.