What are the compression options for storing large amounts of text in Postgres?
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/