KGB Archiver is the compression tool with unbelievable high compression rate. It surpasses even such efficient compression tool like 7zip and UHARC in terms of the abilities. Unfortunately although its powerful compression rate, it has high hardware requirements (I recommend processor with 1,5GHz clock and 256MB of RAM as an essential minimum). One of the advantages of KGB Archiver is also AES-256 encryption which is used to encrypt the archives. This is one of the strongest encryptions known for human.
I tried it out. Have to agre, its has the BEST compression ratio so far! I’ve seen it compress around 1.4 GB (Office 2007 beta) to around 1.5 MB! But it uses a LOT of RAM, and is painfully slow 😛 Anyway, more tests here.
Get it here.