I'm going to try and summarize a lot of the discussion in this post. As has come forward in various threads a lot of the build depends on the user's personal preference, but at least the majority of us agree that some skills should be staple, namely:
[skill]death blossom[/skill][skill]moebius strike[/skill]
These are the skills that make Assassins such awesome AoE damage machines. Due to our low AL it's generally unwise to dive in first, but once engaged we're free to mow down just about anything. Armor-ignoring damage ftw!
[skill]critical agility[/skill]
More attacking means more (Critical) hits, which translates into more damage, adrenaline, and energy. The first cast usually lasts through the entire fight. Don't leave home without it!
Now for my stuff. Don't worry, plenty of it is optional and I'll try to discuss variations.

Attributes
Critical Strikes 12+1 (gloves)
Dagger Mastery 12+1+1 (mask)
--- Critical Strikes should be at 13, the threshhold for maximum energy gain as you will be CONSTANTLY hitting stuff if you're doing it right. Maxed Dagger Mastery without sacrificing HP for it.
--- Some people make use of a third attribute line, commonly for utility skills. Dropping 1 point of Dagger Mastery for this (getting the 3rd attribute to 6) is viewed as most ideal... 2 points becomes niggly.
Weapons
15^50, +30, Zealous Daggers
15^50, +30, Ebon Daggers
+5e, +30, Furious Spear/AR+10v.cold, +30 Shield
+5e, +20%ench, Vampiric Longbow
--- A 15^50 req. should not be hard to fulfil. Zealous is your standard combat set, swap to defensive set when out of combat etc. Ebon Daggers are more for eventualities (eg, baddies with AL+Xv.physical). Instead of 15^50's, 15^ench'd work just as well in most areas.
--- AR+10v.cold Shield is purely because EotN features a lot of Cold damage.

--- Longbow for pulling. +20%ench comes in handy sometimes, and there's already a dedicated defensive set.
Armor
Full Survivor (+1 Dagger Mask)
+1 Dagger rune, +1 Critical rune
Sup Vigor, 2 Vitae
--- In my opinion, there are really only 2 choices for any Assassin: Radiant or Survivor. My experience has taught me it's best to stack up on HP:
- we have awesome energy management available.
- more natural HP gives your Monks a nice big buffer to get you out of danger after a nasty spike.
- following the above, it also means you don't have to spend precious time and skill slots on crap self-heals.
--- Do note that this is also why I would advise against Major/Superior attribute runes. The bit of extra damage does not justify the HP sacrifice (as you will be forced to retreat more often).
The general build I have settled on (note careful wording
[golden fox [email protected]][wild [email protected]][save yourselves][death [email protected]][moebius [email protected]][critical [email protected]][critical agility][asuran scan]
~~~ [skill]golden fox strike[/skill][skill]wild strike[/skill]: mainly chosen for their quick recharge and unblockability.
--- On the subject of leads/offhands, there are 2 different 'schools of thought' if you will:
- Faction A's PoV: 'Kill stuff ASAP.'
- Faction B's PoV: 'Deal as little damage as possible with your intro for DB/MS - you will get more Blossoms in - thus increasing overall pressure damage.'
~ This last assumption, of course, largely depends on someone's personal play style.
...I suppose then there's guys like me, who don't really care... as long as their attacks are guaranteed to connect
Variations befitting
- Faction A: [skill]unsuspecting strike[/skill][skill]golden fang strike[/skill]
- Faction B: [skill]golden phoenix strike[/skill][skill]sneak attack[/skill], [black mantis thrust]
The recharge of [[Golden Phoenix Strike] can be a bit of a drag, since stuff tends to die REALLY fast once you start beating, but it's a great way of freeing up a slot. Be aware that enchant strips will shut you down, however. [[Black Mantis Thrust] comes into its own on bars featuring [[Asuran Scan]... not many other Hexes are worth a spot.
Special mention goes to the Lead-[skill]exhausting assault[/skill][skill]moebius strike[/skill][skill]death blossom[/skill] chain - at the cost of immediate frontal damage, you get an interrupt. Very nasty in the hands of a good player. Due to the early Dual, this chain is great at charging [[Save Yourselves!] too.
~~~ [skill]critical eye[/skill]: a very nice overall buff. Prime contender: [skill]critical strike[/skill]
--- Most agree additional energy management is needed. No, wearing Radiant armor is not the answer. Why I chose Eye over Strike:
- You don't have to be chaining to benefit from it.
- If you ARE chaining, you don't have to sacrifice an opportunity to Blossom.
- Unstrippability is veeery nice.
~~~ [skill]asuran scan[/skill]: insta cast hex that sends your single-target DPS flying beyond comprehension. Blossom's AoE damage is NOT increased, so if you're going for mob pressure you might not want to use it. That's difficult, I know.

~~~ [skill]save yourselves[/skill]: this skill is what made me go /W.
--- From r3 onwards, it's without a doubt the best party support skill available to you, at r7 it can be maintained 100% no problem with only minor investment in your Hero set up. I wouldn't say it's mandatory, but if you're going to swap this out... you'd better have a DAMN good reason. Ask your Monk sometime.
Other good skills:
[skill]you move like a dwarf[/skill][skill]finish him[/skill][skill]club of a thousand bears[/skill][skill]shadow sanctuary[/skill][skill]pain inverter[/skill][skill]brawling headbutt[/skill][skill]light of deldrimor[/skill][skill]sneak attack[/skill]
[skill]assassin's remedy[/skill][skill]critical defenses[/skill]
commonly seen defensive buffs
If you're comfortable giving up [save yourselves] (for example, when pairing up with an Imbagon friend):
[skill]mystic regeneration[/skill][conjure frost][conjure lightning][conjure flame] or the ever-so-awesome [grasping earth] (if only we could pack it as A/W
--- Note: do not overestimate the Conjures, especially in HM. The extra damage is NOT armor-ignoring, and speccing off your 2 main attributes will either compromise your energy maintenance (spec off CS), or decrease AoE damage to adjacent foes (spec off DM).
--- Since its PvE un-nerfing [skill]mystic regeneration[/skill] once again enables Moebius farming. You need Earth Prayers to be at a hefty 8 for this, so the yellow numbers aren't going to be as pretty.
...
... so yeah. GFL y'all.