Test.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;

public interface A
{
}

public abstract class BaseA : UserControl, A
{
}

[System.ComponentModel.DataAnnotations.Display(Name = "B")]
public class B : BaseA
{
}

[System.ComponentModel.DataAnnotations.Display(Name = "C")]
public class C : BaseA
{
}

public class MainForm
{
	private readonly Dictionary<string, Type> _types = new Dictionary<string, Type>();

	private UserControl _myControl;

	private void Initialize()
	{
		var types = GetTypes();

		foreach (var type in types)
		{
			var name = GetName(type);

			_types.Add(name, type);

			// Add to your menu
		}
	}

	private static string GetName(Type type)
	{
		var attribute = type.GetCustomAttributes()
			.Where(x => x is System.ComponentModel.DataAnnotations.DisplayAttribute)
			.FirstOrDefault();

		return attribute == null ? type.Name : attribute.Name;
	}

	private static IEnumerable<Type> GetTypes()
	{
		var types = typeof(MainForm).Assembly.GetTypes()
			.Where(x => !x.IsAbstract && x.IsClass && typeof(BaseA).IsAssignableFrom(x))
			.ToList();

		return types;
	}

	private void MyOnMenuClick(object sender, EventArgs args)
	{
		// Find out which button got clicked, which name it has.
		var name = "";

		var type = _types[name];

		var instance = (BaseA)Activator.CreateInstance(type);

		// Dispose the old control
		_myControl.Dispose();

		_myControl = instance;

		// Time to start displaying the new control
	}
}