should have been faster Raghunathan answereded faster than me. His method is good, mine allows to have the button state at any moment (the interrupt will run even when doing stuff :-)

Nice approach also
I though about something else, i designed a debouncer on MAX5032 programmable logic chip, so there should be components that do the job for you (well don't use a max5032 which doesn't exist anymore and costs a buch of green bills for just a button) but it is also an idea

Regards,
Benjamin