Sorry I haven't been on much, we've been busy:
http://www.neogaf.com/forum/showthread.php?t=738136
I'll just assume you missed all of June, then;
Dragon Bash
A temporary, dragon themed holiday. The only substantial permanent addition was Moa Racing in Eastern Lion's Arch.
Sky Pirates of Tyria
A temporary dungeon (Aetherblade Retreat) was added, and now appears as a fractal, along with a new Aetherblade jumping puzzle in Gendarran Fields. AOE Looting was added. There was a pretty substantial skill and trait balance update, including a new condition called "Torment" that causes more damage to moving targets. Necromancers were much improved. Gifting was added to the Gem Store.
Bazaar of the Four Winds
This was one of my favorite updates. Added a new, temporary zone (Labyrinthine cliffs) that had a lot of cool vertical climbing sections. Lots of little lore tidbits about Glint (a major character from GW1). A new permanent activity (Sanctum Sprint) was added, along with a new mini-game (Belcher's Bluff). The achievement UI was overhauled, and with it came new Achievement reward chests that you unlock at specific milestones (including some unique skins). They also added a new crafting material (Quartz) and a PVP Map (Skyhammer).
Cutthroat Politics
Players used special Support Tokens to vote for two candidates, which determined what content would appear in a later update (just added in November). Two temporary PVP activities were added (Southsun Survivor, Aspect Arena), along with a Horde Mode-like instance called Candidate Trials (also temporary). Three new armor skins were added to the gem store (Braham's, Magitec and Phoenix).
Queen's Jubilee
The collapsed section of Divinity's Reach was rebuilt and featured a temporary, large-scale arena (Crown Pavilion) and a bunch of really cool (and really tough) 1-on-1 boss fights (Queen's Gauntlet). Champion rewards were overhauled, making them much more rewarding, and a bunch of new Exotic weapon skins were added. A new Wallet was added that condensed all of the various currencies (gold, dungeon tokens, karma, etc.) into one account-based menu.
Clockwork Chaos
Introduction of Scarlet. Large scale, zone-wide invasions began to occur across the game world with substantial rewards. These are still on-going but occur much less frequently and I believe people have generally stopped going to them. PVE culling was removed.
Super Adventure Box: Back to School
SAB returned, though it was overly difficult and not very well received. New SAB skins, as well as a ultra-tough version of the SAB (Tribulation mode). Magic find was removed as a stat on gear and was instead made an account-wide feature. New "Essence of Luck" items that drop (or can be obtained via salvaging) will permanently increase your magic find across all characters. Ascended crafting was added, allowing weaponsmith, artificer and huntsman to reach level 500 and produce ascended weapons. Legendary weapons were updated (new visual effects for some, re-writable stats for all).
Tequatl Rising
Tequatl encounter substantially improved, now requires a coordinated effort from a large amount of people. Many world bosses were improved as well, making the much harder. Looking for Group tool added. Ruins of Power added to WvW.
Twilight Assault
A new permanent path was added to the Twilight Arbor dungeon. WvW performance bonus chests, new Hairstyles, Living Story achievements.
Blood and Madness
Most of last year's Halloween content with a new mini-dungeon added for the Bloody Prince's storyline. Balance changes to traits and skills, new combat UI options for targeting and condition damage indicators. WvW season 1 started.
Tower of Nightmares
A large section of Kessex Hills was revamped, with a huge tower occupying the lake with lots of huge vines growing out from it. Lots of new events added to the area. A new heal (Anti-toxin spray) was added for all professions. New armor skins added to the gem store (phalanx, viper, trickster)
The Nightmares Within
A very large (three floors) and very difficult zone was openned in Kessex Hills, sort of an open-world dungeon. Several new skins, including Marjory and Kasmeer's weapons to the Gem store.
Fractured
The Fractal that players voted for way back in July was added, along with fractal versions of the Molten Facility (April) and Aetherblade Retreat (June) dungeons. The final bosses from those dungeons were also added as new boss fractals. Fractal levels became account-wide instead of character specific.New "Mistlock instabilities" were added to make higher-level fractals harder (mixed results) and the way Fractal loot is handled was changed.
That brings you up to Wintersday 2013, which is most of last year's content along with Ascended armor crafting and another balance update.
