Shadowmere is a hero character, meaning that you can not kill him. Since he is an animal you can loot him when he is knocked unconscious. You can also stock up items on him and they will stay on him throughout the game until you knock him out and remove them.
The steps to do this are as follows:
1. Get Shadowmere (Fort Farrgut) and knock him unconscious (kill him).
2. When he is laying on the ground you can open his body like any normal corpse.
3. Place any items you wish to transport into his corpse's inventory.
4. Let him get up and then go and take him wherever you want.
5. To get the items back you can knock him out and take them out. They never disappear.
You can have items in him for as long as you want. Even if he respawns back at the Fort Farrgut he will still have your items on him.

To do this you need a horse and the more expensive the weapon you wield the better.

So get your most expensive weapon and wield it. Get on your horse and fast travel to either Kvatch to speak to the orc merchant, or to Silver Road in Cyrodill and speak to a merchant in green clothing.

Once you enter the barter screen, sell your equipped weapon. It will not vanish, allowing it to be sold over and over again for gold.

This no longer works after a recent June patch to the game.

First you have to complete the Cure for Vampirism mission, and talk to The Count, Janus Hassidor. When you talk to him, ask him about the "Reward" conversation option, but don't leave the conversation, and keep asking him about it. Everytime you ask him about it you receive 1000 gold (or more depending on your level). Do this as many times as desired for unlimited gold. Note that a recent June patch has fixed this glitch.

Any time after you have finished the tutorial in the imperial sewers at the start of the game, you can kill a specific person and loot unlimited amounts of gold from them. Here's how you do it:

In the Imperial City, Talos district, find a house owned by a person named Dorian, it will be called "Dorian's House". Try to get him angry enough with you via threatening him. Once he has a low enough disposition (lower than 20) with him, he will ask you to leave. At this point kill him and go to loot his body. He should have around 40 gold and some other misc items. LOOT ALL THE ITEMS FIRST leaving the gold, DO NOT LOOT ALL. When you go to take the gold, it will glitch and keep allowing you to take the gold off him. Make sure he doesn't leave or alerts any of the guards and save before attempting this. After about an hour of hitting the same button, I had 150k gold. Note: You can bribe him before doing this glitch and you'll make more gold. This no longer works after a recent June patch to the game.

First you must have completed the Thieves Guild quests without destroying the Boots of Springheel Jak. In order to do that you must simply survive a small fall near the end of the last quest with the boots unequipped.

After that go to the Shrine of Sanguine and get the quest there. Follow what the quest tells you to do and when you cast the spell, guards will try and arrest you. Get arrested. (Don't worry, all your equipment is in a chest at the Shrine of Sanguine, so you shouldn't lose anything.)

After you serve your time, you should have the Boots of Springheel Jak in your inventory. If you try to equip them, it will say "You can not equip this enchanted item at this time." But if you check your Active Effects page under Fortify Acrobatics, it should say that you still have the boost from the boots. You can also feel free to equip any other boots as well.

1)Equip ANY set of arrows.

2)Draw your bow back,while its drawn back press B to go to your inventory screen.

3)Click on the arrows you have equipped with A and then on any other set of arrows you own and press A twice.

4)Now find an item you wish to clone and drop it. This doesn't work with every item.

Note that a recent June patch fixed this glitch.

Paintbrushes have no physics applied to them. By none, I mean none. When you drop them out of your inventory, they stay in thin air. They cannot be moved or blown away by spells/arrows.

Well, paintbrushes can be walked on.
You can jump onto a paintbrush (there is a small sphere of invisible walkable surface area). Drop another paintbrush infront of you, and you have a second step.
You can make a staircase of paintbrushes and, ideally, reach any point of the game. The catch? It's not easy to pull off.
If you jump too far, you'll be on the steep side of the walking area and won't be able to jump to the next paintbrush. Also, the walkable area is very small.

This glitch can get you high places like the top of a castle, high in the air randomly, or even on top of the Imperial Palace (watch out, the roof isn't solid, you need to stand on one of the things that stand up out of it).

To see through almost any wall, first you will need a magic staff of any kind. Deplete the staff's uses to 0, then face the wall and walk up to it and attack it, when you attack it you will be able to see what is on the otherside. Ideal for caves and such.

1. Pull out any weapon(including fists)
2. Attack(Pull right Trigger)
3. Switch to inventory before attack ends(B button/red)
4. Equip any set of arrows and press A until a message, "You cannot change weapons while attacking" appears.
5. Drop Item you wish to Dupe
6. Exit Inventory and collect Duplications.

Note:
~The following cannot be duplicated; Stolen goods, one-of-a-kind items(Normally named something), Nirnroot, & Quest Items.
~The number of arrows in the set you equip will be how many the item becomes(at least)

When you go into Frostcrag Spire go to the teleport pads that lead you to the Living Area, go to the portal on the right side and stand on it. Then save the game. Go to your XBox 360 HD and delete the Frostcrag Spire Download. When you load your file it will say "You are loading a file that is missing data". Click yes then load the game. You will be floating. If you look around you will see house. Run forward while pressing jump rapidly at the same time until you teleport into the building. Once you exit the building go to a fireplace outside you will see a weapon called "The Mace of Doom". Developers intended for it not to be in the game because of it's power but you now hold control of it. Go into a building where you see a sigil stone at the top. Approach the top until you are in front of the sigil stone take the sigil stone and get out as quickly as humanly possible. You will obtain 2-4 of each of every sigil stone if you get out very quick. Once outside teleport to any city. Congratulations! You now have multiple copies of every sigil stone and the Mace of Doom!

NOTE:
1. In order to do this you must have the Frostcrag Spire Downlaodable Content.
2. Once deleted you can redownload Frostcrag Spire for free.
3. Make sure you take anything you have in Frostcrag Spire out becuase if you don't it will be permanently gone.
4. Bring at least 3 Paintbrushes with you and do the paintbrush glitch so you can reach the Sigil Stones.
5. Do not bring any other items besides Paintbrushes so you do not become Over-Encumbered taking the sigil stones because they produce very rapidly in your inventory and you may get 600 encumbrance in 15 seconds!
6. Make sure you have extra save files in case you mess up!
7. Be patient while getting to the house when you're floating. For me it took a good 2 or 3 minutes so be patient!

Equip any set of arrows, go into any area of the game (preferably an enclosed area, like a fighter's guild basement), take out any bow, and hold R to keep an arrow in your bow. Now, you have to be a journeyman(?) of acrobatics, but if you can combat roll, that's what you need to do this trick. Hold L, press Y, and move in any direction to roll. You will hear the arrow fly, but it will not decrease in your inventory. Go forth and pick up your dupe arrow. Repeat as many times as you like.

This glitch allows you to easily repair and/or recharge items (armor, weapons, and staves) without having to carry around hundreds of pounds of hammers and soul gems, or having to visit a merchant in town all the time.
STEPS:
1: Have any item
2: Duplicate the item so you have two of them (or just buy an exact duplicate, but rare items have to purchasable duplicates)
3: While the items are UNequipped, go to the menu and hotkey them (there should be 2 of them) to any one of the hotkeys.
4: Use item to your heart's content (damage the item in some way)
5: Unequip the item using the hotkey button again. Then press the hotkey button one more time to re-equip it.

The item has been repaired and recharged. Go to your item menu to check it out for yourself. This works unlimited times, and as long as the item can be duplicated (or you can buy an exact duplicate) it should work.