The following are most standard builds that are commonly used with short description.
Player versus Player
Classic "Bomb" build (http://is.gd/ICwsBQ)
Probably more popular during 1.6 patch series this build strongly focuses on delivering massive detonation damage. This can be deadly versus under geared opponent.
Avatar Hybrid/General (http://is.gd/qzFhOH )
While packing a little less punch than classic "bomb" build this variation brings supreme protection against knock backs making it deal choice for larger scale pvp such as minigames. With this build you can pretty much go entire 20 minutes of the minigame without being knocked back even once (rotating excellent balance and avatar).
Lotus Hybrid/General [reverse hybrid] (http://is.gd/2r68e5)
This build switches the focus of the end tree feats on Lotus side which results in slighly less physical resilience (due to loss of HP leech from avatar), but has an advantage of a superior anti CC abilities. With both Lotus Overdose and Excellent Balance running you are virtually immune to every CC in game.
Some swear by "tribrid" builds as being the best for PVP. With this one you will lose some of the spike in damage, but gain access to more anti CC feats.
Player versus Environment (solo)
Solo PVE Hybrid for Khitai (http://is.gd/x7u1TL)
This is perfect build for leveling up in Khitai. At first you will need Atrophy to "soften up" your opponents a little.
Solo PVE Hybrid for Khitai [advanced] (http://is.gd/ICwsBQ)
As you get better gear your can switch to this build for faster killing. It is "bomb" build so it can be used for PVP as well. With avatar running and detonation and both DWW/GB you can leech absurd amount of health to out-live any mob in Khitai.
Solo PVE Hybrid for Khitai [kidney shots] (http://is.gd/bLgRV4)
This is my current build. With maxed out AA tree and brittle blade set I have a lot of offhand so I have decided to further upgrade my build with offhand chance. I am using kidney shots to to stack them with other damage buffs to create...pretty much a ball of death. My combo is the following: kidney shots + avatar + liberation + gray lotus + path of enlightenment. With this I can survive absurd pulls or by pass intended game mechanic for solo bosses in hardmode/unchained versions of dugeons (like killing Accalia in her camp in DMH unchained).
Player versus Environment (dungeons)
Avatar Hybrid (http://is.gd/Y3tNJ7)
This is a build for longer fights and it provides both sustained damage and a nice spike. You need a good tank and gear/perks for this or you will over-aggro. Good build for clearing up dungeons that have trash mobs (like AOK).
In this build you still get to keep some of the spike damage (DWW/GB) but your are getting a major upgrade to your anti aggro.
Player versus Environment (raids)
Overkill (http://is.gd/66s6Bs) by Shahir of Destiny Crom EU
If you are looking for more laid back raiding experience or (like me) getting constantly aggro in raid encounters this build will "fix" it all. If you also have cover of the dusk perk then you have 5 very potent anti aggro tools at your disposal which will make up for lack of skill/gear/bad tank. In more extreme situations you can also use this build in group dungeons.
Classic Raid DPS, Magic Based (http://is.gd/fsYYRc) by Shahir of Destiny Crom EU
The supposed "golden standard" of raid speccs that will put you on top of the DPS charts. Tried and true.