Getting all types that implement an interface

Question

Using reflection, how can I get all types that implement an interface with C# 3.0/.NET 3.5 with the least code, and minimizing iterations?

This is what I want to re-

Answer 1

This worked for me (if you wish you could exclude system types in the lookup):

Type lookupType = typeof (IMenuItem);
IEnumerable lookupTypes = GetType().Assembly.GetTypes().Where(
        t => lookupType.IsAssignableFrom(t) && !t.IsInterface);