All gliders in competition are required to use Flarm, I would think 90%+ of the others would use it as well. It works quite well, it would be great if more GA and RAA aircraft would use it. It is relatively cheap and can be linked to moving map displays.
Sunny, be sure to get an Australian frequency powerflarm as unlike the others powerflarm is specific to Aust, US or Europe. A European one will display you to gliders here but not display them on your display.