Where do I find real GPS data to test with?

I am developing tools that works with gps data on mobile devices. I would like more data to test with and I wonder if there is any good resource out there to fetch such data. It could be gpx-files, geojson or any other format.

In my experience the gps data from mobile phones are much more varying in quality than what I get from an iOS or android simulator and I would like to have more realistic data to work with. Real recordings would be the best.