EPSG:900913
It took me a while, but now my geocaching map is online. It lists all geocaches found by team ItTakesTwo (Liz, Anja and me) troughout the world. After fiddling with EPSG:4326 (WGS84 geographic data) and EPSG:900913 (unofficial spherical mercator projection used by Google and others) you can now see the map on this website. It is based on the great OpenLayers framework and uses Cloudmade OpenStreetMap and Google Maps data for basemaps, while the caches are pulled in from an GPX file.
I hope to update the map regularly.