How to load plugins in .NET?

I'd like to provide some way of creating dynamically loadable plugins in my software. Typical way to do this is using the LoadLibrary WinAPI function to load a dll and calling GetProcAddress to get an pointer to a function inside that dll.

My question is how do I dynamically load a plugin in C#/.Net application?

The following code snippet (C#) constructs an instance of any concrete classes derived from Base found in class libraries (*.dll) in the application path and stores them in a list.

using System.IO;
using System.Reflection;

List<Base> objects = new List<Base>();
DirectoryInfo dir = new DirectoryInfo(Application.StartupPath);

foreach (FileInfo file in dir.GetFiles("*.dll"))
{
    Assembly assembly = Assembly.LoadFrom(file.FullName);
    foreach (Type type in assembly.GetTypes())
    {
        if (type.IsSubclassOf(typeof(Base)) && type.IsAbstract == false)
        {
            Base b = type.InvokeMember(null,
                                       BindingFlags.CreateInstance,
                                       null, null, null) as Base;
            objects.Add(b);
        }
    }
}

Edit: The classes referred to by Matt are probably a better option in .NET 3.5.