Septim (Coin)

The Septim is the main currency in all of Tamriel. It is named after the dynasty that rules the Septim Empire founded by Tiber Septim. It is officially called a Septim due to the bust of Tiber Septim on the obverse side. The legend on the obverse (front) is: "The Empire is Law. The Law is Sacred." The reverse reads: "Praise be, Akatosh and all the Divines."

Other names
It is colloquially known as Drakes due to the seal of Akatosh on the reverse side. The in-game name of the item is actually Gold, but NPCs, books, and anything else outside the game menus refer to them as Septims.

Acquisition
Septims can be found on dead enemies and in containers, found lying around, obtained through completing quests, (amount may depend on level) selling items, and from being stolen or pickpocketed. In PC versions of and, septims can be added via the   console command, where X denotes the desired portion.

Oblivion
At the Imperial City, max out Dorian's disposition and strike him with a Paralysis-inducing effect, such as those found in spells, poisons, and weapons. Search his body and remove the 227 present there. Unlike normal looting, the remains in his inventory and can be collected infinitely. Collecting it for roughly ten minutes yields 1 million, while nine hours yields 50 million. (This exploit was fixed by the 1.1.511 patch.)

Thieves Guild
The Thieves Guild in Riften has more than one set of Thieves Guild Armor in the The Ragged Flagon's Cistern which can be picked up. A full set is in the lockpick training room, with three more pieces scattered throughout the cistern. The armor is valuable due to its enchantments. The armor will respawn an infinite number of times.

Skeleton book
There is a glitch in Skyrim involving an infinite number of books found on a skeleton which can be sold. This can be found above the Sightless Pit near Winterhold.

Mannequin duplication glitch
Placing valuable apparel, including but not limited to Daedric, Dragonplate, Dragonscale, and even Dragon Priest Masks, on mannequins in purchased homes results in a doubling exploit. It involves placing the chosen armor on the mannequin, removing it without exiting the screen, then leaving the house and re-entering. Take the armor found on the mannequin and repeat. Sell the duplicated items to a merchant.

However a more recent update has patched this on the 360 version.

Arrow stealing
Several shooting ranges feature archers shooting at targets. All arrows fired at the targets can be collected and sold. The archers have infinite arrows and can be pickpocketed. when you Pickpocket you can put in different Arrows and archers will shoot those Arrows. This is a quick and easy way of farming expensive arrows or rare arrows, like a Daedric Arrow.

Shrine of Mehrunes Dagon
The Shrine of Mehrunes Dagon, once cleared, will respawn its many gold and ebony ingots, along with valuable enchanted armor, etc. after about one week in the game.

Blood on the Ice
When visiting Calixto Corrium on Blood on the Ice, it is possible to sell him the Necromancer's Amulet and then pickpocket the amulet in order to then sell it back. Each successful attempt is rewarded with 500 gold and a large amount of Pickpocket experience. (No Pickpocket perks are required.) Once Calixto's house is left, it will remain open for the rest of that day, but will lock and stay locked (Master) from then on, but Calixto has a key that can be pickpocketed or taken off his corpse. He will not be in there ever again and the contents out in the open on shelves, etc. respawn (enough to complete a Bedlam job for Delvin).

Balimund

Balimund in Riften can be pickpocketed  for his gold and then you can buy items from him then pickpocket the gold he has again and again until you have all the gold that he owns then you can wait 3 days (72 hours) and then repeat. Then you can sell the items you have gotten from Balimund.

Trivia

 * An actual replica of the Septim coin was included in the Collector's version of .Coin.jpg