Convert a shapefile (.shp) to xml/json

GDAL is your friend. Use the ogr2ogr libraries, and here's a cheat sheet.

If you want a good GIS application, install QGIS and download the gdal converter plugin

I've found this website that converts loads of Geo formats: http://mygeodata.eu/apps/converter/index_en.html

In less than 2 minutes I was able to convert a ShapeFile zip to a GeoJson file!

(I was trying GDAL at the same time and it's still downloading...)

What dassouki said. Get GDAL from http://www.kyngchaos.com/software:frameworks. Use it to convert a shapefile to GeoJSON like this:

$ ogr2ogr -f "GeoJSON" output.json input.shp

eg

$ ogr2ogr -f "GeoJSON" /tmp/world.json world_borders.shp world_borders
$ cat /tmp/world.json
{
"type": "FeatureCollection",
"features": [
{ "type": "Feature", "properties": { "CAT": 1.000000, "FIPS_CNTRY": "AA",
  "CNTRY_NAME": "Aruba", "AREA": 193.000000, "POP_CNTRY": 71218.000000 }, 
  "geometry": { "type": "Polygon", "coordinates": [ [ [ -69.882233, ...
  ...