valid timezone abbreviations/displaying timezone value?

I have a timestamp column that I'd like to display in a user-defined timezone
with:

select updated at time zone $TZONE from page;

where $TZONE is a PG-valid timezone abbreviations.

1) Does anyone have a list of valid timezone abbreviations?

2) Is there a way to get the timezone to display in the above select for each
row returned? (it only shows if I don't specify the time zone)

In general, "at time zone foo" seems to be a rather poorly documented command
-- the only mention I can easily find is in the _Practical Postgresql_ book,
where it says "PostgreSQL supports the use of all ISO standard time zone
abbreviations" (p.76). That would be helpful if I could find a list of
standard ISO time zone abbrevs -- Google yielded
http://greenwichmeantime.com/info/timezone.htm which doesn't have abbrevs for
all timezones and PG doesn't seem to accept timezones in 'GMT+X' notation...

Thanks for any help or pointers,
Adi