Unfortunately, there is no "best" application for the categories you gave. Everyone seems to have a slightly different preference. From what I know, here are the recommended applications for each of the things you gave:

PIM:
GPE Suite
Pimlico
Gene Cash's Python apps (although, I seem to recall some people saying these have trouble with os2008...)
GarnetVM

E-mail:
Modest
Claws-Mail

Chat:
Pidgin
rtcomm update (extends the built-in google talk client to get on any protocol)

Try them all out! Everyone has a different preference, and they can all (with the possible exception of the rtcomm update -- I've never tried uninstalling it), be easily uninstalled.