I do too ....and sometimes they aren't the straightest. I use my 2 inch punch to punch squares out of photos but would love to find a 3 inch for perfect squares every time!
Be careful of the 3" Marvy punch. They measure diagonally. I have made this mistake with them. The super giga (or something like that- the green one) does 3 1/2 diagonally, but is only 2 1/2 length. I just measured mine.
Its not a punch but if you have a die cutting machine(sizzix, cuttlebug, etc) you might try the spellbinders nestabilities squares. I dont know the exact measurements on them. But there is probably something around that size. They are really easy to use and nothing to worry about breaking.
....and sometimes they aren't the straightest. I use my 2 inch punch to punch squares out of photos but would love to find a 3 inch for perfect squares every time! 
