These are the only ones I know other than the ones you said:
~There are the secret banshees on The Package.
~The mini skirmisher and the secret elite on Winter Contingency.
~Golden Ranger Elites (B.O.B )
~Data Pads
~Radios.
~Flying a seraph.
~Mini phantom
~Mini falcon
~Untextured Master Chief of Lone Wolf.
~Master Chief cyro tube.
~Cube glithes in phantoms.