What Do I Query to Get Space and TempSpace Information?

This query:

SELECT
  Sum(ue.bytes) / 1024.0 AS stg,
  ue.segment_name,
  ue.tablespace_name       
from   
   user_extents ue
GROUP BY
  ue.segment_name, ue.tablespace_name;

is a start, I think. THe user_extents table contains storage information. There's more to it than this, I think, so other answers with more info would be welcome. But I thought I'd post this so that other people who like to experiment (as I do) would have a starting point.

Regarding Temp Space usage - most of the Temp Space queries I have seen center around v$sort_usage which has info on sorts that are currently in progress. I will dig around for a good example.

Try this...

Select d.tablespace_name "Tablespace",
       sum(f.bytes_free) + sum(f.bytes_used) "Total Size",
       nvl(sum(p.bytes_used), 0) "Used",
       nvl(sum(f.bytes_used), 0) "Used HWM",
       ((sum(f.bytes_free) + sum(f.bytes_used)) - nvl(sum(p.bytes_used), 0))  "Free",
       s.initial_extent "Uniform Extent Size",
       sum(f.bytes_free) / s.initial_extent "# Pieces Free"
from   SYS.V_$TEMP_SPACE_HEADER f, DBA_TEMP_FILES d, SYS.V_$TEMP_EXTENT_POOL p, dba_tablespaces s
where  f.tablespace_name(+) = d.tablespace_name
and    s.tablespace_name = d.tablespace_name
and    f.file_id(+) = d.file_id
and    p.file_id(+) = d.file_id
and    d.tablespace_name = :x
group by d.tablespace_name, s.initial_extent
:x(VARCHAR[4],IN/OUT)='TEMP'