All of the point_ entities are just grey boxes as well, this is the list of them:
point_anglesensor
point_angularvelocitysensor
point_bonusmaps_accessor
point_clientcommand
point_enable_motion_fixup
point_gamestats_counter
point_gamestats_counter
point_hurt
point_intermission
point_message
point_playermoveconstraint
point_posecontroller
point_push
point_servercommand
point_teleport
point_tesla
point_velocitysensor
I know some of those have to be used, or at least I think it would make for some interesting things if they do get used.
Ohh, also:
keyframe_track
move_track
info_decal - can have something similar to the overlay?
env_splash
env_smoketrail
env_laser