One which springs to mind for me is a Heavy Infantry regiment.
They get mentioned in several of the 40k novels, and other fluff, not stormtroopers, but regular guards who just happen to wear carapace armour and possibly carry hotshots.
Cadian Karskins are one example off the top of my head, but I remember seeing them mentioned at least 2 or 3 other times in different fluff and novels.
Heavy Weapons squads?
Amphibious?