Found this helpful article I thought I’d post..
http://webpaws.com/blog/2008/08/19/postback-in-aspnet-passing-variables-on-postback/
Basically I had a class variable in an ASP.NET and found it was getting lost on page post-back.. well all you have to do is put that object in the Viewstate object already created for you.

eg:

public partial class MyPage : System.Web.UI.Page
{
        protected int MyInt;

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
		MyInt = 12345;
                ViewState["MyKey"] = MyInt;
            }
        }

        /*
	 This is called on a page post-back...
	*/
	protected void Event(object sender, EventArgs e)
        {
			//Get factor list from viewstate
			MyInt = (int)ViewState["MyKey"];

			//Go nuts
	}
}

As soon as I started using Web Services I came against this problem, and loads of other people have asked it before but I didn’t really find a satisfactory answer. The easiest method is to create your own custom class (or a struct, as I did) and use that:

The struct

public struct KeyValueStruct
{
private int _key;
private string _val;

public int Key
{
get { return _key; }
set { _key = value; }
}
public string Value
{
get { return _val; }
set { _val = value; }
}

public KeyValueStruct(int key, string value)
{
_key = key;
_val = value;
}
}

The web method

[WebMethod]
[XmlInclude(typeof(KeyValueStruct))]
public List<KeyValueStruct>  GetEnergySources()
{
List<KeyValueStruct>  sources = new List<KeyValueStruct>();
sources.Add(new KeyValueStruct(1, "Solar"));
sources.Add(new KeyValueStruct(2, "Wind"));
return sources;
}

Simple!

I know this is old, but I was looking for it and it seemed to be the best solution:

http://blogs.claritycon.com/blogs/steve_holstad/archive/2005/12/22/128.aspx