Xceed Streaming Compression for .NET is an efficient and lightweight data compression class library for Microsoft .NET and ASP.NET. It can process any size byte array with ease and provides a true .NET pass-through stream object for automatically compressing or decompressing any .NET stream’s data on the fly. It supports the GZip, Zlib, Deflate and Deflate64 compression formats.

http://www.xceedsoft.com/products/StreaNet/