I'm in the process of developing a few lists. Here they are so far. If you have any additions, or wish to challenge any of these, bang on the comments as hard as you like. This is a work in progress.
Making these lists is something I'm doing with my daughters as a way of helping them learn to think.
1. Here is a list of everything I absolutely know exists:

• Me (Thank you Rene D.)

2. Here is a list of things we speak of as if they were real, but they do not exist:

• Squares and Circles
  
• 1 dimensional lines
  
• 2 dimensional objects
  
• An inch
  
• The poor*
  
• The rich*
  
• The sky
  
• Perfection
  
• Ten pounds
  
• Infinity
  
• 4
  
• Pacifism
  
• God as any human has described God.

3. Here is a list of things I believe are real, but I lack complete evidence of their reality. Given my first list, I realize this list could include everything in the world except me, but I'm doing this as an excercise for my kids. I think you see where I'm going with this.

• Color
  
• Causality (One thing causes another)
  
• Other people
  
• Right and Wrong
  
• Australia
  
• Yesterday
  
• Love

Australia is a bit of a joke, but it's fun watching the three sisters argue that Australia really exists and deal with their frustration at not being able to prove it. None of us have been there, you see, though there's no place on earth I'd rather go.
4. Here is a list of things I want to be true so badly that I'm willing to act as though they are true all the days of my life.

• God
  
• Goodness 
  
• My Life Ultimately Means Something

I want my daughters to think well, and I want them to think for themselves, ESPECIALLY about the things that everyone assumes are true. I think it's my job to nurture this in them.
It's a joyous thing to watch their minds open like little flowers.
My middle daughter has been questioning me about the existence of God since she was six. It's a good thing to talk honestly with her about what we know, what we believe, and what we are committed to.
Each of the three sisters will choose her own path. While they live with me, I can only show them my life, honestly tell them what I think, live according to my beliefs, and pray for strength to be a good example.

rlp
*There are only individual people in this world. There are people who own a lot and people who have almost nothing, but these categories are only a convenient way of thinking about people.