Proudspire Manor

Located next to the Bards College in the eastern side of Solitude, Proudspire Manor is the most expensive player-owned house currently available in Skyrim.

Acquisition
The manor may be bought for 25000 from Falk Firebeard after completing several tasks for Jarl Elisif the Fair, which is a prerequisite to being made Thane of Haafingar. The Dragonborn needs to have completed The Man Who Cried Wolf quest and a small task for the Jarl Elisif the Fair. The total cost, including decorations, is 36000. Proudspire Manor is the most expensive house from all purchasable houses in Skyrim. Detailed in one of the bugs below, however, the house, and all of its subsequent upgrades, can be bought for free if the player follows the correct procedure.

Upgrades
A selection of upgrades are available for purchase from the Steward after you have bought the house.

Known bugs

 * Bug (PS3) -  when you leave your house you sometimes drop out of solitude and ALL of your followers die. Fixed by loading working save file. PlayStation 3 confirmed.
 * Bug (PC, Xbox, PS3) - ("Fixed", workarounds confirmed: Workaround - Use "Unlock" on console commands; "Fix" - Becoming Thane of Solitude entitles the player to a housecarl, which for some reason unlocks all doors, including the back door.) Sometimes walking out on the patio, after purchasing the upgrade, the door will say "Requires Key" even though you have it, making it impossible to enter through the patio door. Entering through the other two entrances still works.
 * Bug - Upon becoming Thane of Solitude the Housecarl's Quarters in the basement remain an undecorated room and do not become furnished like the Housecarl Quarters in the other homes.
 * Bug (Xbox, PS3) - (Need to confirm whether this was fixed in patch) - The weapons rack and mannequins in the basement which can hold weapons/shields/armor do not always work. Sometime weapons can be put in racks but no armor on the mannequins, and vice-versa. The mannequins tend to dissapear regardless of what you place onto it.
 * Bug - The 5 weapon rack in the basement is only able to accept weapons in the three middle slots. It's unknown if this is a bug, oversight, or intentional.
 * Bug - (PC, Xbox, PS3) Spouses will often sleep on the bedroll in the basement near the enchanting and alchemy tables. This can prevent you from getting the Lover's Comfort buff when sleeping.
 * When you first access the mannequins, if you mount something, then remove it without leaving the inventory screen it will duplicate the item when you leave the house. While this can be useful it also means nothing can be displayed except that item.
 * Bug - (PC, Xbox, PS3) Near the mannequins, there is a texture bug that can appear on the wall behind them.
 * It is possible that when you load a save in the house all your upgrades disapear. This is fixed by reloading your save.
 * Bug - (PC, Xbox, PS3) - The weapons rack in the master bedroom on the third floor will not allow any weapons to be mounted on them at all.
 * Near the weapons rack in the basement, hay floats a few feet in the air above a side table.
 * Because the gold is not immediately removed from the player's inventory, this house can be purchased for free by choosing "I'll Take It," backing out of the conversation, and immediately placing all the player's gold in the cupboard behind Falk Firebeard. No gold will be removed and the key will be given. The Slow Time shout, or the perk Steady Hand (slows time by zooming with an arrow drawn), can be used to make this easier, but neither are necessary. This same technique works for purchasing decorations as well.
 * (Confirmed Xbox 360) This sounds tougher than it actually is, and it does work, at least on the Xbox 360 verision. Getting the upgrades is a bit harder to achieve than getting the house itself, since Firebeard's sentences are shorter after purchasing upgrades than after purchasing the house. Get as close to Firebeard and the nearby cabinet as possible. Saving after each successful attempt also doesn't hurt.
 * Upon going into your house all of your possesions in the home may be scattered everywhere (Xbox)
 * Upon going into your house your possessions that are in the brown "tray" near the enchanter may be scattered everywhere on the floor (PC)