5)A movement I kind of "came up with" one day which really smoked my low back is the following: use a straight bar, feet shoulder width with a "soft" knee (maintain this knee position throughout), and peform a Romanian Deadlift (keep the head up, and shove the butt back and keep a neutral spine).
Keep the bar close to the body, and go down until the bar is at mid-shin (remember, keep the neutral spine).
Once you've reached mid shin with a neutral spine, round out the back slowly until the plates touch the floor.
Now, using only the lumbar muscles, extend back up, slowly and smoothly, into the neutral spine position.
Do not come all the way erect (like when you began the set).
Once you reach neutral spine, round out again and repeat the extension. 15-20 reps. You won't need much more than the bar to start this, and your low back will be screaming after 15 reps. It is kind of an RDL, SLD, Good Morning, and back extension all rolled into one. Try it.
Andy.