Pride - Stormrage (website). Supposedly oldest Guild after Sturmgrenadier (both were active during the closed Beta). See above.
Think Different (website) - Stormrage, EU Servers. A new guild being setup for all levels with an emphasis on mid-levels (30 - 50) to begin with so we can arrange some good learning instances (although, we won't exclude lower or higher than that). /w Rrabetep in-game for more details - it's early days so anyone wanting to join now could have quite an influence on how we develop...