What are the compression options for storing large amounts of text in Postgres? I need to store large amounts of text in Postgres, mainly command logs and the output of long running commands and need to know if there are some settings that could help compress the data transparently with a tool like zlib, or some other native space saving methods.

The data is primarily read only data, so writing is not a problem.
By default Postgres automatically compresses everything TEXT. It uses a simple lzcompress algorythm:

https://www.postgresql.org/docs/9.3/storage-toast.html

There is a plugin that will probably evolve to LZ4 compression support for TEXT:

https://github.com/zilder/pg_lz4

There is a FDW that also support compression:

https://www.citusdata.com/blog/2014/04/03/columnar-store-for-analytics/