Good luck training deads with Coldo, his advice on the the Deads thread was that people bang on too much about form.

I have a weak lower back too but I have found deads have really helped. Mine twinges sometimes for no particular reason and it screws me up for days. Be careful with squats as these put undue strain on the lower back and if your form is a bit off on those it will screw your back, its how mine first went.

With regards to back exercises try wide grip pulldowns to chest, lat pull downs to neck (if you can), close grip pull downs. All variations on chin ups but on machines. If you can do dumbell rows. Once your back is bent over the effeort goes through your arm and upper back so if done properly you shouldn't feel anything in your lower back. If in a posh gym they may have a seated pull/row machine? Opposite to bench presses but you put your chest intot he machine and pull back. T-bars and bent over rows are good but will put stress on the lower back although you should lock your lower back in place when doing these.

There used to be a basic bit of equipment in my old gym that you laid on and basically done the revers of sit ups. No weight needed and it strenghtens the lower back. I have no idea what the movement is called though? Bent over back raises or something I would have thought. You can do this exercise off the end of a normal bench if you need.