looks quite good.
A few other formats it supports and some more info
High compression ratio in new 7z format with LZMA compression
7-Zip is free software distributed under the GNU LGPL
Supported formats: 7z, ZIP, CAB, RAR, ARJ, GZIP, BZIP2, Z, TAR, CPIO, RPM and DEB
For ZIP and GZIP formats 7-Zip provides compression ratio that is 2-10 % better than ratio provided by PKZip and WinZip