Postgres on Engineyard space at 100%, pg_xlog filled up with files
You can revise the checkpoint_segments setting in your postgresql.conf and issue SELECT pg_reload_conf(); as the postgres (super)user (in any database) to make that change live. What the change to that setting does is reduce the number of WAL segments that remain resident in your pg_xlog directory. If you have a lot of data churn in your db you will want to keep the checkpoint_segments setting at 32 minimum (see http://www.postgresql.org/docs/current/static/runtime-config-wal.html#GUC-CHECKPOINT-SEGMENTS for more details).

Some general tips:


Ensure your autovacuum settings are pretty aggressive.
Move the pg_xlog directory to a different volume than the $PGDATA directory. I have measured performance increases from 10% - 30% from that change alone.
Set up a monitoring tool to keep an eye on table/index/database/server size increases. Eg. Nagios, New Relic,