Dead lifts (if with enough weight, they hit your lower back STRONG)
Bent over rows (more like a full, but hits lower back pretty good)
Good mornings (Amazing for lower back,but might need a barbell)
Superman Situps (Just situps, but do them like superman
Back is personally my favorite body part to workout, i have tons and tons of exercises if you need anything else for back, not just lower)
As you might know, lower back and abs are all connected. (just incase you didn't know) All core.
And abs, there's too many.
Besides all the variations of situps and stuff.
You can put a dumbell on you feet and do 6 inches, that adds weight.
Put a weight above your head or on your chest and do situps.