try 7zip or kgb arckiver, those have a high compress ratio, but u cant really compress video, or audio verry well because its already compressed and that most of that has random data
that's right. Audio files, for example, barely compress but I have found that archiving them is still useful if you want to send multiple files to someone. Packing them all together makes it convenient to send just one file.
I believe RAR has some compression level settings where you can set the compression ratio so I guess you could get files smaller that zip if you wanted to but ti would take longer to uncompress
if you have, for example a phpbb forum theme, with lots of files (all the images and stuff), and you copy it somewhere, it sometimes takes a while, even though its just a few mb. if you compress it, its pretty instant. thats one thing i like.