Determine whether a type is simple.

TypeExtensions.IsSimpleType.cs

public static class TypeExtensions
{
	/// <summary>
	/// Determine whether a type is simple (String, Decimal, DateTime, etc) 
	/// or complex (i.e. custom class with public properties and methods).
	/// </summary>
	/// <see cref="http://stackoverflow.com/questions/2442534/how-to-test-if-type-is-primitive"/>
	public static bool IsSimpleType(
		this Type type)
	{
		return
			type.IsValueType ||
			type.IsPrimitive ||
			new Type[] { 
				typeof(String),
				typeof(Decimal),
				typeof(DateTime),
				typeof(DateTimeOffset),
				typeof(TimeSpan),
				typeof(Guid)
			}.Contains(type) ||
			Convert.GetTypeCode(type) != TypeCode.Object;
	}
}

IsValueType returns true for Collections which I don't want. I just removed it from your condition and used it.

That seems to do the job for me:

public static bool IsPrimitiveType(Type type)
{
    return (type == typeof(object) || Type.GetTypeCode(type) != TypeCode.Object);
}

I found it on the same page on stackoverflow by the way. It has less overhead and is way simpler.

This variant will not return true for Guid, DateTimeOffset and possibly others.