This forum contains threads for every guild on Project 1999, but there's one problem: the forum has no "overview", so you have to click through every guild's thread individually.
To make the guild-finding process easier the Project 1999 wiki offers a
Guild List overview page. This page groups the server's guilds by type (casual, raid, and top-tier raid), and includes basic information about each guild in an easy to compare tabular format (eg. their loot policy, voice chat policy, what classes they're recruiting for, etc.)
Hopefully this page will make it much easier for you to find the perfect guild.
NOTE #1: Once you find a guild that you are interested in it is recommended that you still read their Guild Discussion thread (there will be a link to it on the wiki page). This is because the forum thread may have further (or more up-to-date) information about that guild that the wiki.
NOTE #2: Guild leaders and officers: if you wish to update your guild's information in the wiki please see the instructions at the bottom of the page. The page now uses templates so it is super easy to do so even if you are not a wiki person.