<p>BITS, the Windows background intelligent transfer service.</p>

<p>Looks like there are a few C# wrappers around that manage the interop to BITS, does anybody have any opinions on the best one?</p>

Check out the following:
http://www.codeproject.com/KB/cs/Managed_BITS.aspx
http://www.simple-talk.com/dotnet/.net-tools/using-bits-to-upload-files-with-.net/