Throughout Skyrim there exist a number of standing stones for you to discover.  Each of them may be activated singly for personal benefit (as what benefits one character may not be of use to the entire party).  Each character may benefit from only one Stone at a given time but may freely switch between Stones by returning to a given Stone and having its' power overwrite your currently active power.

Below is a list of Stones and its' corresponding benefit:

Apprentice Stone: Regenerate PP at 50% faster rate; 25% additional damage from magic

Atronach stone: Power Point total x1.25; Spell damage absorption 25%; Recover PP at 0.75 rate

Lady Stone: recover ExhP at 1.25x; Regenerate health at 1.25x (also benefits from spells)

Lord Stone: physical damage x0.9; +20 RR vs magic

Lover Stone: Learn any 4 selected skills faster*

Mage Stone: Learn 10 selected magic-related skills faster **

Ritual Stone: 1x/day Raise all dead within 50' to fight for you for 10 rounds

Serpent Stone: 1x/day Paralyze target for 1 round and cause 25 points of poison damage, RR applies

Shadow Stone: 1x/day become invisible for 10 rounds

Steed Stone: Armor worn encumbers as AT-1; Carry weight subtracts 50lbs before encumbrance is calculated

Thief Stone: Learn 10 selected thief-related skills learned faster **

Tower Stone: 1x/day automatically pick one non-magical lock

Warrior Stone: Learn 10 selected combat-related skills faster **

*  Reduce all DP costs by 1 (for example, 2/5 becomes 1/4)
** Reduce DP cost by 1 of the second and third numbers for any skill (for example, 2/5 becomes 2/4)