hi friends, sorry my english is a little bad.
In the last quest of the mage's guild, if you make the choice : offering the girl at Sheogorath, you'll get a book who give you 2 skill points.
The exploit :
You can do this quest with as many character you want and transfer the book to your bank to give 2 skill points to your main character and thus get a lot of extra skill points.
I'm pretty sure that this quest does not have a minimum level required. (i've do it at lvl 30 with my reroll)
Enjoy