What is a good title for an early hire at a startup who is really the CEO/Co-founder's right hand person?

Chief Administrative Officer; Chief of Staff. Suggestion - do not worry about the title too much in this early stage. After six months your true role will be clearer.

Many small companies are actually moving away from titles, or using titles that are non-standard.

Sometimes mystery in a title can bring on a conversation, which ultimate direction can be very rewarding...

COO

Concur with that suggestions. Alternatively, in a "small" startup, the earlier hires can be referred by the sequence in which they started with the company, #1, #2 etc.. no titles. As part of onboarding, new employees should understand the roles of the individuals (absent titles).

Chief Administrative Officer, Chief Operations Officer. The disadvantage of not having a title is that if you are the "right-hand person" of the CEO/founder, you are going to be dealing with a lot of key outside individuals and companies; and the proper title lets them know that you have the authority to make decisions and enter into business relationships.

In start-ups and small companies, titles are more for the outside world than internal use.