What are valid values for the MediaType Property on a HttpWebRequest

What are valid values for the MediaType Property on a HttpWebRequest?

I want to do something like this:

Dim url As String = HttpContext.Current.Request.Url.AbsoluteUri
Dim req As System.Net.HttpWebRequest = DirectCast(System.Net.WebRequest.Create(New Uri(url)), System.Net.HttpWebRequest)
' Add the current authentication cookie to the request 
Dim cookie As HttpCookie = HttpContext.Current.Request.Cookies(FormsAuthentication.FormsCookieName)
Dim authenticationCookie As New System.Net.Cookie(FormsAuthentication.FormsCookieName, cookie.Value, cookie.Path, HttpContext.Current.Request.Url.Authority)

req.CookieContainer = New System.Net.CookieContainer()
req.CookieContainer.Add(authenticationCookie)
req.MediaType = "PRINT"

Dim res As System.Net.WebResponse = req.GetResponse开发者_StackOverflow社区()
'Read data 
Dim ResponseStream As Stream = res.GetResponseStream()
'Write content into the MemoryStream
Dim resReader As New BinaryReader(ResponseStream)
Dim docStream As New MemoryStream(resReader.ReadBytes(CInt(res.ContentLength)))

Thanks.

I think this wikipedia page should give you a fairly comprehensive list of media types:
Media Types