As demonstrated in the Skill Template format and as seen at Guild Wars Wiki:Game integration/Skills, every skill/effect in the game is assigned an ID code for identification by the game engine. By using client-side memory editing tricks, it is possible to make the game display any skill in the game on the skill bar in the Skills and Attributes panel, and thus view the name, icon, description, and other statistics of the skill. (This does not allow you to actually use any skill in the game: this can only be performed in an outpost, and there are checks in place to remove any "disallowed" skill when you leave an outpost.)
Data for all skills in the game is available below. Each page is an index of 500 skill IDs with the skill name. If the skill already has an article on the wiki, the name will link to it and have a green background. Those that don't have articles will have a red background.