A number of new assertions classes have been added to MbUnit since the latest post on this topic.  The new helper classes involve Arrays, collection, compiler, serialization, web...

ArrayAssert

This helper class contains method to compare arrays:

byte[] expected = ...;
byte[] actual = ...;
ArrayAssert.AreEqual(expected,actual);

The method compares the rank, the length and makes element-wize comparaison.

ColAssert

This class provides several methods to compare two ICollection instance:

ICollection expected = ...;
ICollection actual = ...;

ColAssert.IsSynchronized(actual);
ColAssert.AreCountEqual(expected,actual);
ColAssert.AreEqual(expected,actual);

The class also provides method to test the collection count, syncroot, synchronization, etc...

SerialAssert

This class contains various methods to test the "serializability" of objects.

SerialAssert.IsXmlSerializable(typeof(MyClass));

WebAssert

This class contains assertions on the properties of web control and web pages.

CompilerAssert

This class contains assertions to check that snippets are compilable:

String source = ...; // C# code to compile
// verify that source compiles
CompilerAssert.Compiles(CompilerAssert.CSharpCompiler, source);

What about your assertions ?

There is also a CodeSmith template that can let you build "strongly-typed" assertion classes out of existing types. See in the templates directory.