• Earn experience the old-fashioned way;
• Restoration spell, which means going to a Patriarach/Matriarch like Zekon and paying or agreeing to a geas-enforced task for the casting;
• Rare items like a wish;
• Purchasing experience from Agamnenar, The Wraith King guy with the trained wraiths - they can breathe a level into you for a price.

Having experience input into you by a wraith feels wrong to me, like installing software on your computer that comes from a crooked hacker. No matter how clean they pledge the software is, you can never really trust that your box has not been compromised…