All the sudoku puzzles you could ever want – many variations from Nrich.
I really like the #OCRmathsPuzzles, look out for them.
For a puzzle with a difference that requires both logic and multiplication try a Find the Factors puzzle from Iva Sallay on her Find the Factors blog. In this Find the Factors 1-10 puzzle can you place the numbers 1 to 10 in the first row and the first column to make the multiplication table work? Iva Sallay has clearly explained the puzzles here: How to Find the Factors.
New puzzles are published each week, I like the Excel files provided with puzzles of varying levels of difficulty. You will also find many hints and tips in the various posts. See Hooked on Factoring, for example, a post giving techniques for solving the puzzles and an Excel file of puzzles.
Paul Godding’s 7 puzzle blog offers new puzzles to try daily.
Erich Friedman’s Puzzle Palace includes an extensive collection of puzzles including many requiring mathematical skills.
Yohaku is a puzzle that will test your number sense and problem-solving skills. Each Yohaku puzzle is either an additive or a multiplicative puzzle. You must fill in the empty cells such that they give the sum or product shown in each row and column as well as satisfying a rule if given.
BrainBashers offers a large collection of puzzles and brain teasers, there is also a section on illusions.
Puzzlemadness.co.uk – all the puzzles you want – no apps to install!
On Futoshiki.org from Vlad Daskalu, you can generate puzzles of sizes from 4×4 to 9×9 and choose one of 4 difficulty levels.
Other sites offering these puzzles include Brain Bashers.
Nick’s Mathematical Puzzles (Nick Hobson)
For very attractively presented Puzzles (and Games) – try Mathigon.