The best library around is IMO AL "Advanced Library for Poser". And it's free! It also works with P8 and PP2010. It is very fast, has preview images, search function, can load stuff (via PRPC) directly into poser and much more.
P8 and PP2010 doesn't work for me with the current library, so this can be an alternative for those who have problems or just want a library that are not a part of Poser. I do have ShaderWorks Library Manager but find AL to be better for my needs.

Some links.
To turn off the flex library in P8/PP2010:
http://www.renderosity.com/mod/freestuff/details.php?item_id=57157

Advanced Library for Poser:
http://neocron.lunarpages.com/library/

PRPC - to get stuff loaded from AL in to poser:
http://prpc.sourceforge.net/