Since the recent update completely changed how Assassin's work in AoC, I will post some new Assassin builds designed for different reasons.

Raiding/PvE Build: This is the way I have Callesto feated as of right now. The damage done overall has yet to really be tested in a raid, but the overall base dps is increased from before the update by 12 points. Utilizing the combat rating (unholy) increase of the initial Corruption tree is what improves that base dps. It gives the general feats for stamina regen (vital for long fights) and snare/root break and knockback prevention for the occassional PvP encounter, but other than that, this build is focused entirely on high dps and high volumes of damage per attack. The lengthier the battle, the more damage the DoTs add up to, which helps make this an ideal raid spec.

PvP/Soloing build: This build makes use of the Corruption tree's ability to buff your melee attacks, debuff your enemy's defenses and do high short bursts of damage which makes them ideal for fighting PvP. High burst damage ensures an early advantage on your foe, letting you take advantage of the natural assassin abilities that do quality damage over the remainder of the fight. The charging ability, repeatable fearing combo, and natural physical defense debuff associated with their attacks makes them a very fierce and competitive fighter in the open playing field. It is complete with general tree abilities to break root, fear and prevent knockback. Also a small increase to hiding and hide movement to ensure a bit more ease in stalking targets. This is the format my pvp assassin, Oryana, will follow.

Hybrid Raiding/PvP build: This build utilizes the best benefits from both corruption and lotus trees, ensuring good damage done during raids, plus the debuff and burst damage properties of corruption. It also makes use of every possible CC from both trees aside from the final abilities in each tree (Lotus gets an AoE fear and Corruption an AoE stun as their final feats). Having a fear, a stun, a knock back, a charge plus all the CC breakers is a great way to ensure your foe in a PvP battle field dies well before you do. However, the lower damage done than pure lotus, the lower burst damages than pure corruption, and the lack of any good personal buffs from either tree leaves you more as a jack of all trades but a master of none. Still a quality build that I plan to switch Callesto to in a couple weeks.

White Sands PvP build: Because the update got rid of stances, it is no longer feasible to go all general tree at a low level. It leaves your damage dealt far too low. You now have to feat into either lotus or corruption to be able to deal quality damage in a fight. So what I've done here is gone all offensive and ignored all the defensive feats of the general tree. This gives you both the weapon damage increase of lotus and the combat rating increase of corruption, while increase critical hit rate, giving the corruption miasma attack to enable a lengthy stun (you have to use slow death strikes first) and gave you the Atrophy combo which does a fair amount of damage while lowering the targets damage output. You can substitute the lotus feat points for more critical damage in the corruption tree, but I'd not recommend it.

Level 39 minis build: Much like the white sands PvP build since the update, it is difficult to find a perfect set up that allows for quality offense, defense plus CC breaks. So what I've done here is maximize base dps by feating lotus and corruption, increasing critical chance and critical damage to further the pure damages done, and ensure access to all CC breakers which are important in PvP.

Level 59 Minis build: This build utilizes the same general tree set up as the 39 minis build, allowing full access to all CC breakers. However, it hybrids between corruption and lotus to raise total damage done with critical rate/damage bonuses from corruption and some offhand attack rate increases from lotus. It makes snap kick available and utilizes the lotus tree ability to increase soul fragments, which is stronger than corruption's equivalent (lotus gives 4 instantly, corruption gives 4 over 16 secs). It also gives the Corruption tree's miasma as it seems to be a bit stronger for PvP aspects, but you could easily swap for lotus's if you prefer.

*These builds may be followed, but it's always better to use them to get ideas and alter them for your own style of play*