Kakuro Online
From the home page: Kakuro puzzles are similar with crosswords, but instead of letters the board is filled with digits (from 1 to 9). The board's squares need to be filled in with these digits in order to sum up to the specified numbers. You are not allowed to use the same digit more than once to obtain a given sum. Each Kakuro puzzle has an unique solution. Good luck!
2048 Game
From the instructions page: 2048 is a single-player puzzle game. The original idea was contributed in March 2014 by Gabriele Cirulli using an inspiration of the 1024 app game. The purpose of the game is to dictate a sequence of arrow movements on a 4x4 board with the purpose of reaching the 2048 value on the board. See more instructions here.
KenKen Puzzle Official Site
This is essentially the same as Kakuro. This site has lots of ads and flashing stuff, but does have a free interactive KenKen puzzle on the home page to play, and even ways to make your own puzzles.
Cross-Number Puzzle Maker from WorksheetWorks
From the home page: The cross-number puzzle replaces the words in a crossword with numeric digits, and math equations replace the word hints. The larger the puzzle you select, the larger the maximum size of the numbers that go into the grid, as well as the more difficult the math problems. You can select the kind of math problems to use, so this puzzle can be made to be solvable by students who are only proficient with their multi-digit addition skills. This is a good math crossnumber puzzle generator, but you have to print the puzzles out to play. I have had some printouts available during the course.
Play Cross Number Puzzle from MathIsFun
Very simple on-line crossnumber puzzles. Mostly references to other clues.
Acrostic Puzzles by Puzzle Baron
From the homepage: An acrostic puzzle is sort of a hybrid between a cryptogram and a crossword puzzle. Your goal is to reveal a hidden quote in the grid at the top by correctly answering the crossword-style clues near the bottom of the puzzle. Each letter in the quote is linked to a letter in one of the clue answers. As you fill in more and more answers, more letters will begin to fill the quote grid, until eventually the entire quote is revealed. What's more, the author and/or source of the quote will be spelled out when you read the first letter of each answer.
1Sudoku
From the homepage: Although the classic 9x9 grids are the most common, there are several variations of sudoku. There are size variants (larger grids type 16x16 or smaller type 4x4 for children), Sudoku variants with irregular regions, with mathematical or logical constraints. There are also alphabetic sudoku variantsas wordoku which use letters instead of numbers. Nice interface to the puzzles on this site.
Yohaku
From the homepage: A yohaku is a new type of number puzzle that will test your number sense and problem solving skills. Each yohaku is either an additive or a multiplicative puzzle (as indicated by the symbol in the bottom right of the grid). Your task is to fill in the empty cells such that they give the sum or product shown in each row and column. I really like this variation of the kakuro and kenken puzzles, themselves a variation of sudoku. Allows algebra and fractions!!
Daily Online Set Puzzle
Make 3-oblect sets from a total of 12 entries in this puzzle. Harder than it looks. The 3 objects need to be totally different or the same. I find it challenging and addicting.
Insumnia
This is an addicting little puzzle created by my former company, Learners At Play. Get close to or hit the target number by placing arithmetic operators between the numbers. Use the options for more interesting play. Have fun!
Transum Math Puzzles
All sorts of math puzzles, mostly pretty simple and a little hokey, but fun.