Don't forget about DynamicMethod.  You can create a delegate to an arbitrary
method, constructor, or property accessor anywhere... and it works lots
faster than the Invoke on MethodInfo via reflection.  (You can cache
delegates in a dictionary, for example, and have the ability to access
properties or methods by a string name)

There is an introduction to this type of thing on a CodeProject article:
http://www.codeproject.com/csharp/DynamicMethodDelegates.asp?print=true

There's also something on MSDN about it, but it's not very helpful.

If you want to get really fancy and use generics that determine their type
parameters at runtime, then you'll have to do something like this :
http://musingmarc.blogspot.com/2006/08/how-to-do-late-dynamic-method-creation.html (Marc is one of my newfound hero's)

I found http://www.west-wind.com/presentations/dynamicCode/DynamicCode.htm 
to be a pretty good reference on doing this.. put me right off the idea :)
You could also use the Script control (though you'll have to use vbscript or
javascript) - Add a reference to the COM \ Microsoft Script Control 1.0 and
do like..

 <snip>
 ScriptControl script = new ScriptControl();
 script.Language = "vbscript";
 script.AddObject("joe", new ken(), true);
 Response.Write(script.Eval("(1 + 3) * joe.bob"));
 </snip>

 [ComVisible(true)]
 public partial class ken
 {
   public int bob = 3;
 }

..too easy!

Regards,
Eliott