MultiFormPoster is a .NET 3.5 class library for creating form POSTs which are commonly used for accessing
web APIs. This is typically done with the WebClient Upload file method but that class doesn't give you the 
flexibility to add more name/value parameters to the form POST.

Usage:

using ThirtyPoints.MultiFormPoster;

// If you're going to be uploading a file, you'll need to first read it in as a byte array
FileStream fs = new FileStream("c:\\test.jpg", FileMode.Open, FileAccess.Read);
byte[] data = new byte[fs.Length];
fs.Read(data, 0, data.Length);
fs.Close();

// Generate post objects
Dictionary<string, object> postParameters = new Dictionary<string, object>();

// Adding a file as the post parameter Be sure to add the content-type as well
postParameters.Add("file", new FileParameter(data, "test.jpg", "image/jpeg"));

// Adding a normal name/value post parameter
postParameters.Add("name", "FileName");

// Create request and receive response
string postURL = "http://linktotheplaceyouwanttopost.com/link.html";

// Create an HttpWebResponse object and use either the MultipartFormDataPost WITH Basic HttpAuth params or without
HttpWebResponse webResponse = FormUpload.MultipartFormDataPost(postURL, "UserName", "Password", postParameters);

// Process response
StreamReader responseReader = new StreamReader(webResponse.GetResponseStream());
string fullResponse = responseReader.ReadToEnd();
webResponse.Close();
// Do something with fullResponse. This may contain xml, json, or whatever the API you're posting to is using.


ToDo:
1. Add ActiveDirctory auth?
2. Add cookie container (some sites authorize you based on the cookie they already dropped)

Credit: This class is based heavily on a blog post by Brian Grinstead which you may find here:
http://www.briangrinstead.com/blog/multipart-form-post-in-c

I've taken his example and blown it out a bit to add some functionality such as basic http auth functions.