3% HP or Bust

Items

Armlet of Mordiggian is the item to get on Huskar. I recommend rushing Armlet directly after Boots of Speed for best results. I'm not a fan of Urn of Shadows on Huskar (it delays your Armlet of Mordiggian and provides unnecessary Mana Regeneration), but the option exists if you can't stand having those two Gauntlets of Strength sit cold turkey until your Core Items are done.

Post Armlet of Mordiggian, purchase Power Treads -> Helm of the Dominator -> Black King Bar and/or Heaven's Halberd. Your choice of Black King Bar or Heaven's Halberd should be carefully selected in response to enemy team's composition. If the enemy has both heavy Magic and strong right clickers (or hybrid carries such as Morphling, Luna and Shadow Fiend) then purchasing both Black King Bar and Heaven's Halberd is encouraged.

From there, the best luxuries for Huskar tend to be Heart of Tarrasque and Satanic, mostly because +Strength is the best itemization available to Huskar. Win or lose, most games should be over by the point you have Heart of Tarrasque and Satanic. If not, you should look into one of Assault Cuirass (if your team has other carries and no Assault Cuirass yet), Monkey King Bar (if the enemy team has any of Heaven's Halberd, Butterfly, Phantom Assassin, Riki, Brewmaster or Windrunner) or Daedalus (if none of the other conditions apply and you'd like to crit for 1000+).

Gameplay

Huskar is best classified as a durable semi-carry who can both gank and initiate with Life Break. I advise laning either solo mid or with a support in your team's safe lane (bot for Radiant top for Dire). In lane your priorities should be farming > harassing/trading hits > denying. Try to avoid leaving your lane to gank until you've at least farmed your Armlet of Mordiggian.

The most important rule to remember when playing Huskar is to be a man. If you are a man while playing Huskar, you have already won half the battle. The other half of the battle tends to lie in correctly executing the all-in-one sequence listed below this paragraph. If you don't have the item needed for a step, skip it:

1. Use Inner Vitality (on self)
2. Use Life Break
3. Toggle Armlet of Mordiggian
4. Use Black King Bar
5. Attack
6. Use Heaven's Halberd
7. Use Satanic (when HP is low)
8. Untoggle -> Toggle Armlet of Mordiggian (for 475 burst HP when you have a window below 475 HP)

Successfully feigning death is a core ingredient for making big "I just 1v5'd with 20% HP" plays with Huskar. Note that Inner Vitality is reactive and will double if you drop below 40% HP regardless of what your HP was when it was applied. The most common mistake I see Huskar players make is that they do not apply Inner Vitality to themselves before leaping into a team fight and then either forget to use it or waste 0.3s (Inner Vitality's cast time) doing so mid-fight.

Lastly, you are not buying Helm of the Dominator merely to justify skilling Stats. Remember to use its Dominate ability every time you can (keep in mind Dominate's 300s/5m recharge time) to amass an army of neutrals for the purposes of stacking, buffing, or assisting in ganks for you. Prioritize Centaur Khans (War Stomp, +AS Aura), Dark Troll Warlords (Ensnare) and Frost Ogres (Ice Armor) with Dominate.

Replays

Coming soon!

Changelog

9/18/2012:
Remade the step-by-step sequence in "Gameplay" into a list. Also (and more importantly), replays are coming soon!
8/27/2012:
Sections ("Skills, "Items, "Gameplay") upgraded into Chapters.
8/26/2012:
Guide published.

If you have any comments, concerns or suggestions regarding my guide, I encourage you to PM them me or post them below.