I run a Life based Ethereal Knives build.
I chose this build because it requires no quality gems, and all of the gems used are easily obtainable. The main damage comes from the gems themself, and the Hatred aura, so little specialised gear is required.
The linked gems I use are: Ethereal Knives + Faster Casting + Added Fire + Iron Will + Blood Magic.
I plan to add Faster Projcetiles should I get a 6 linked chest. The Item Rarity can replace Added Fire or Iron Will should you want to try and farm for items, and the Life Leech gem can be used for harder content. If you feel your cast speed is lacking you can drop Faster Projectiles and use Faster Castining a 4link, but your pack clearing speed may decrease. An interesting choice would be the Empower Gem, adding substantial DPS due to how EK scales with gem level. The drawback however is that it takes a very long time to level up, meaning you won't really get to use it until you're around lvl 88.
You will need to play as a Shadow or Witch to Mud Flats to get the Ethereal Knives gem however. A quick 5 minutes isn't a bad investment.
The auras I use are Grace and Hatred. With a level 10 Reduced Mana, and the Sovereignty nodes in the templar tree I was able to run two auras and still have enough Mana to use Enduring Cry and my Curses. You could run Clarity on your life using Blood Magic if you are lacking some Mana Regen, but I found the little you get in the passive tree is enough.
I have a 4 linked trigger gem set up. I am using Cast when Damage Taken + Summon Skeletons + Molten Shell + Blind. The Cast When Damage Taken is level 12 and triggers when I take 1500 damage. It automatically casts Molten Shell to give me more armour, and two skelly bros pop up to take the heat off me if I need to recover. Blind is a very nice addition for when Molten Shell breaks and hits lots of enemies around me. The Skeletons can also blind enemies they hit. This has been an extremely powerful defensive combo for me so far, along side my Endurance Charges. You can also switch in Life Leech instead of Blind (although it would require a Chromatic or...50), as Molten Shell gets pretty strong at higher levels... and Elemental Reflect could pose a problem.
Unfortunately the Cast When Damage Taken gem is only available in Merciless Act 3, but I was using Cast When Stunned before to a similar effect but it wasn't as reliable.
For the bandits I helped Oak in Normal for the Life, helped him again in Cruel for the Physical Damage, and then helped him AGAIN in Merciless for the Endurance charge.
I like Oak.
I am currently level 85 in the new Nemesis league and my current build is this:
I started with all the HP and Life Regen, then taking the Aura nodes, Iron Reflexes, Elemental Adaptation, Endurance Charge and the Spell Damage (in that order). I will take the Block Nodes last of all.
The tree focuses on easily obtainable Life nodes and Life Regeneration so I can use the Blood Magic gem for my main skill. I have 300% maximum Life and 4.7% Life Regen. I have the Keystone Iron Reflexes and the aura Grace as well as a Granite Flask and Molten Shell to give me lots of Armour, and I plan to have 5 Endurance Charges for more flat physical reduction, and boosting Elemental Resists in Elemental Weakness maps.
This was my tree to level 50:
After which I continued up to get Purity of Flesh and then started down into the Duelist/Ranger area.
This is a completely different build to the EB / Aura / Arctic Armour build that is popular on here, and I feel a much easier one for a new player or a new league. Please leave any constructive criticism, or experiences you've had with mine or a similar build. Thanks for reading!