What methods are there to to regain sanity?

There are a lot of ways to regain sanity. Excluding the Hallucination-killing ones, that require you to lose sanity due to the Insanity aura, here are some powerful ways that let you recover quickly:

• Sleep in a Tent (+50 Sanity)
• Sleep in a Straw roll or Fur roll (+33)
• Repair a Relic (+20)

These are quite easy to do, and more powerful than any food-eating or flower-picking method.

Anyway, for a complete list of Sanity recovering methods you can head to the Sanity page on the wiki.

Sleeping using a straw/fur roll or using a tent increases sanity by a significant amount. Eating candy or (most) food from the crock pot also increases sanity a bit. For more detailed information you should go to http://dont-starve-game.wikia.com/wiki/Sanity.

You can make a garland out of 11 petals and it will slowly increase the sanity