Sending object to ToJSON()

I'm using the helper method outlined here:
http://weblogs.asp.net/scottgu/archive/2007/10/01/tip-trick-building-a-tojson-extension-method-using-net-3-5.aspx
So my question is, I want to send a pair of values.  So something like this:
"key" : "<img src...>"
right now, I'm only sending in a List<string> to that method.  I'm not quite sure what type of object that I could use as List<string> obviously only allows me to send one value


So what kind of object could I pass if I want to get a key in here?  Maybe a dictionary of values?  I know that if you were to pass in an object with properties, the helper would convert the properties to key value pairs in the JSON returned.  But here I am creating an object and not sure what to use.

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