A starting point to find the basics of a checklist (which should then be rigourously checked against the contents of the POH, as previously stated) is at
this site. I don't know which flavour of PA28 you were in, but there are a variety available here.
I have recently done a checklist for our club Fuji FA200, which is not a million miles from a PA28 in terms of equipment, etc, but the sort of thing which does need close scrutiny is all the critical speeds, etc.