A photography portfolio is no different than an art portfolio.
It is a vehicle to show the extent of both the technical and aesthetic quality of the work each artist is capable of producing, consistently.
There is only one acceptable kind of work to place in your portfolio ... perfect!
No where should there be any over or underexposed, out of focus or blurry images. They need to show detail in both the highlights and shadow area. If black and white images, they need to have been printed by the artist to show the extent of their technical skills.
The first thing you need to know is why are you putting together a portfolio? Get work in a certain field of photography? If so the portfolio or book should be of images that the prospective employer uses in their course of business. If it is for acceptance to an art school, it should show a complete range of the photographers current abilities. I think by now, you are getting the idea.
When approaching an advertising agency or publisher, it is common to leave a CD of the portfolio that my be of interest to them. In the end, you may end up with three or four different portfolios which target certain segments of the economy.