Need help on drivers, add-ons

Folks,

For a variety of projects, I'm trying to assemble a list of "currently
essential" add-ons to PostgreSQL. However, I'm starting to have sympathy
for PG newbies; as a core team member I can't figure a lot of this out. For
example:

Which C++ driver is most current?
Which python driver is the most full-featured?

But getting to the point is:

What PostgreSQL add-ons do you think are essential for at least 50% of
potential users?

--
Josh Berkus
Aglio Database Solutions
San Francisco