How do I cure Sanguinare Vampiris?

If you're fast, you can chug a Cure Disease potion or pray at a shrine.

Once Vampirism has set in however, you only have two options:

You can become a Werewolf.

or

If you harass enough bartenders for rumors, they will tell you about a fellow named Falion in Morthal who is working on a cure. He'll want Black Soul Gems though, so it won't be cheap or easy!

In Dawnstar I think next to the mine there is a hidden chest (under ground) which when you look at you can open, it is FULL of goodies, which you can sell. One of them is a weapon which when you kill someone with it it actually fills the soul gem for you, a quick short cut. The vampirism is very annoying.

One other thing, when you go to be cured, make sure you have fed on blood before hand otherwise he won't cure you and will instead fight you. Best go to a farm wait to dark, take off your armour and sneek in whislt they are asleep