For when regular giants just don't cut it, here's a few rapidly growing cannibal giants that also have shadow magic.
They come in three sizes, though this does not indicate any kind of progression. Rather, a dusk giant's size is dependent on how many beings it's recently consumed (bonus points if those are sentient).
In my opinion, the potential to on the one hand quadruple your HD because you ate 720 GP worth of beef, and on the other lose half your levels because you're in a construct-filled dungeon is just too unbalanced to allow: for that reason dusk giants will receive an asterisk and will not be assumed to possess Cannibalize. Perhaps a DM could allow it as an alternate mode of progression, but giant HD with occasional ability and armor boosts don't seem worth it to me.
With that out of the way, on to the monsters!
Least Dusk Giant
Medium-sized giants (one of the few ones, aside from stuff like half-giants and forest trolls), with 6 RHD and some pretty neat stats. They have three natural attacks (bite/claw/claw), but according to the statblock can use none when wielding a weapon (I'll assume this is a typo, and that the bite at least can be used).
They also get to Rend after hitting with both claws, which is probably going to drop off in usefulness as magic weapons become more appealing.
Finally, least dusk giants are surrounded by an aura of shadowy illumination that also imposes a -2 penalty on saving throws (amusingly, this secondary benefit is completely irrelevant for the least variant).
Is this worth +0 LA? The stats are pretty good, RHD are literally inferior to a warrior, and natural weapons are non-existent, and what little use the shadow aura has for helping out casters just doesn't justify spending six levels on it. -0* LA on this one.
Lesser Dusk Giant
Large size this time, with more speed, more NA, stronger natural weapons, a much higher strength score, Rock Throwing, and even some minor SLAs (Enervation and Ray of Enfeeblement 1/day), but ultimately not anything worth taking the 12 giant HD for. -0* LA again.
Greater Dusk Giant
Even more size and strength gains (to an impressive 48 strength, much more than any PHB giant has), as well as a ton of SLAs, but I honestly don't think it's worth the 18 crappy RHD. -0* LA.
Feel free to discuss those ratings: I wouldn't be surprised if +0*s are argued for anywhere.