I have written last two posts on founders/co-founders. There are few more things I would like to write about, so thought it will be great to make a check list. First of all, whether you need a co-founder is itself a big question. This post is not a discussion about that question. I will try to address that question in a separate post. This post is about things that you should look for in a person before starting a venture, from a very India perspective. Checklist - 

1. Piggybacker - Is he trying to piggyback you? If yes, then may be he should not be an entrepreneur, but more of an non-executive member of the team who is just providing some financial support to the team. Call him an angel if you want, but not a co-founder. Details about such piggybackers can be found here.
2. Daydreamer - I have discussed this point thoroughly too, and you can read it here. So if s/he is one of those daydreamer, then may be not a good idea to have him/her in the team.
3. Vision - How far can he see? Can he think ahead of time for the responsibilities he will be shouldering? For example, if he is going to be technology head in the company, can he see where geek community is moving? Can he be one of those person who will lead the community in right direction? 
4. Social - I strongly believe that you can not create culture in the company. You and your founding teams personality is directly reflected on the team. So if your founding team is not very social, your company will not have lot of social aspects. People will be just coming and working there with out much of interaction. I dont prefer such companies. Hence I would like a co-founder who is social like me.
5. Sacrifice - Taking financial risks and career risks in one thing. But sacrifice even some part of personal life is a big thing. If your co-founder is going to be attending each and every family event with out even considering current work pressure then he is not a good fit. One of my mentors and a serial entrepreneur told me a very good story about himself. When he started his first company, his wife was pregnant with their first child. Yet he used work from 7am to 2am everyday including weekends! Now he is very successful with millions of dollars. I am not saying everyone should make such sacrifices, but there has to be some. Its a tough thing to be an entrepreneur, no matter how hard you try there are going to be taxes on your personal life. You cant talk to your girlfriend for hours and still be part of next big thing you know.
6. Reason - Why a person is looking for entrepreneurship? What is a driving force for him? What keeps him awake at night? What will keep him motivated in the journey when your burst you tyre/s ? If money is the only reason, then dont even consider him. Most important reason I would look for is does he drive to be the best in what he does.
7. Comfort zone - Lot of people have tendency to get into comfort zones. With hints of even a small success such people will start underperforming big time. They will start spending lot of money too. Plus since they cant be fired from the company, that puts them even deeper into their comfort zones. This attitude will soon be reflected on people who work directly with them and so on. Not a good fit. An entrepreneurs needs to be agile in bad times but equally (in fact more) agile in good times. Momentum needs to be carried forward and forward.
8. Originality - Some people are original in their thought process initially. But after a while since they are not may be reading things, learning new stuff or not interacting with peers/mentors, they lose their originality. Does your co-founder have a drive to find solutions to problem on their own? Is he original enough and does originality drives him? 
9. Team person - Its absolute essential for him to be a team person. He should be work for the betterment of the team. Any thing and everything he can contribute to the team, should be contributed. If he is going to keep things to himself, then team as whole is never going to grow. Also fluid discussions in the team are not going to happen if he is not a team person.
10. Brand - All co-founders will typically be leading few parts of the company. How big is your own brand in what you do? If you are in technology, are you respected as a programmer/architect? Great people wants to work only with other great people. Does your co-founder have ability to create brand for himself to attract such other great people?
11. Decision maker - Last but most important, does he have confidence to take all important decision on his own. Typically an ideal co-founder is some one who can run the company completely on his own without you. 

There are few minor things left unsaid in the post, but above mentioned are the bullet points with which you should evaluate choices you have for co-founder.

Note- I will be using he/him to refer to people and that should not be considered as me being sexiest.