I loved these magnets when I saw them on tipjunkie! Such a great tute and so easy to make. I don't do much scrap-booking so I don't have much left over paper, but I used anything I had to hand- magazine piccies, origami & letter writing paper, old stamps, even the inside of old envelopes. The cardboard from an old box rather than coffee sleeves. I also painted mine with clear nail varnish as I can't get hold of modpodge.
One tip: wipe your sewing machine needle with an wetwipe afterwards as it does get a bit sticky from stitching through the double sided tape and you don't want it to be all gluey for the next time you sew.