I think the .crd files that COWPIE uses are good. They just put the chords inline in brackets. There is software to print up files in this format with the chords on top.

There is also software to convert ABC files to sheet music. It has the advantage of also being capable of being played, but it has the disadvantage of being harder to write. They can include the melody as well as the chords.

If you don't mind the extra work, I would like to see ABC files posted. Otherwise I can happily live with .crd files

Murray