If you need more compression options than provided by the .NET SDK, this might be something for you: #ziplib (SharpZipLib, formerly NZipLib).

This library supports compression/decompression of Zip, GZip, Tar and BZip2 formats. It is a .NET assembly written in C# and useable in any .NET language. SharpDevelop users already know this library, being a part of that open-source .NET IDE.
#ziplib is released under the GPL license, but with an important exception, allowing you to use it in a wide range of applications. For further details on this topic, please refer to the ICSharpCode homepage, where you can download the library. The download contains a help file in .chm format.

SharpZipLib Homepage