These may be less reliable than diaries or letters since they are usually written long after events occurred and may be distorted by bias, dimming memory or the revised perspective that may come with hindsight.  But, they may be the only source for certain information.

Henry Kissinger's Years of Renewal is an example of a marginally reliable memoir.  Most people who write their memoirs write them with their image in mind.  If I were to write my memoirs, there are definitely some things that I would either leave out entirely, or change slightly, just to make myself look a little better and smarter.  That is human nature -- and that is why memoirs must always be read with a little skepticism.  But they are still primary sources.

Here is a book that chronicles a period of time with speeches and writings that are concrete, not interpreted at a later date.  In it's unpublished form, this would have been a manuscript. 

This book is a participant's perspective and analysis of historical events written at the time of the events.  This can be biased, but is a good account of a point of view of the time.  This book can also go in the "Published materials written at the time about an event" section.

Discussion Question:  Wouldn't all primary sources biased in some way?