I've run some tests using PHP's gzcompress() and gzdeflate(). They both work reasonably well, return strings (so I can just siwtfly add it to the code when inserting/retrieving info from the DB), and are fast enough even for constant use (IMO).
I'm shooting for 70%+ compression with a very low toll on the server. gzcompress() seems to be faster than gzdeflate().
Of course, the down side is that I wouldn't be able to use MySQL to execute queries on that info, but I'm not storing it for that purpose anyway.
Here is a test page I put together:
http://www.netbulge.com/misc/test_page2.phpI do notice something strange, the gzcompress() lvl5 seems to be faster than both lvl1 and lvl9.