The 7-Zip compression utility is an open-source project mainly developed by Igor Pavlov, and it provides excellent compression ratios, far greater than those in most compression utilities such as the one in Windows Vista. The four articles here focus on using the 7-Zip executables in a programmatic way.
7-Zip Command-Line Examples
7-Zip DEFLATE Compression Ratios
7-Zip Executable Tutorial
PPMd Compression Benchmark in 7-Zip