Infima Ultimate Archiver claims to be one of the best compressors out there with 10%-85% better compression than existing softwares like WinZip or WinRAR. It also supports standard formats like ZIP, BZIP2, GZIP, TAR, TAR.GZ, TAR.BZ2, ISO and RAR (read-only) and has a familiar Windows Explorer type interface to navigate files.
You can check out their benchmarks on the homepage of the software. I haven’t tried this for videos but audios and pictures certainly compress better than WinZip. The software is in Beta and you have to unfortunately register on their site to download the beta.

Infima Ultimate Archiver