Find it at http://www.codeplex.com/DotNetZip .
New features!! password support is here! Whoohoo!! This is PKzip (weak) encryption. Another new feature: you can now add entries into zips using content from streams. There are clearer exceptions generated in the case of errors. Beyond new features, there are a bunch of other improvements and fixes to the library, too. For example, the internal handling of zip files now uses streams for more optimal memory usage. As another example, there is now a large set of unit tests that ships with the library. As a result, reliability is significantly higher than in v1.3. Finally, the Zip utilities have been updated for better command-line parsing, more options and flexibility.
That's the v1.4 library, which is released and final.
For v1.5, I'll be focusing on Update capability - the ability to update an entry in an existing zip archive with new content, as well as the ability to Remove entries in existing zip archives. There's a preview of the v1.5 library already available on http://www.codeplex.com/DotNetZip .
If you want some background on the Zip Library, check out my prior posts on this topic. Just for your information, DotNetZip is licensed under the Microsoft Public License, which basically means you can use it free of charge, for any purpose, but there's no warranty. Check the full terms of the license on the CodePlex site.
As always if you have questions on usage, check the CodePlex forums.