ZRAM if you have no HDD/SSD swap partition.
ZSWAP if you do have a HDD/SSD swap partition.
ZCACHE: It does what ZSWAP does and ALSO compresses and speeds the filesystem page cache. (It is internally much more complicated and is not in the mainline kernel as it is still under development).
D. Abadi, S. Madden, and M. Ferreira. SIGMOD '06: Proceedings of the 2006 ACM SIGMOD international conference on Management of data, page 671--682. New York, NY, USA, ACM, (2006)
E. Vogel, B. Fierro, F. Bachmann, and G. Saravia. Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)
T. Strutz. 4th International ITG Conference on Source and Channel Coding, (2002)source code available from http://www.embl-hamburg.de/~tilo/Software/CoBALP.tar.gz.