If I deadlift over 400 my grip gives out before my back. If I shrug over 300, same thing. Heavy dumbell rows, my grip will also give out before my back. I might pick up a Caprain of Crush Grip strength tool to help me.
Which are the ones to get, they have a lot.http://www.ironmind.com/ironmind/opencms/Main/straps.html
Grippers don't really translate well to strength to hold a heavy barbell/dumbbell, oddly enough. For that, I've always had three main suggestions -
1. Fat bar training, easiest way is to get some Fat Gripz handles (should be easy to locate online) that snap over a BB/DB and turn it to a thick 2" diameter to work the grip harder. Thick bar work hits the entire hand structure big-time and to most, has the greatest carry-over to all other grip-related work.
2. Pinch grip training, while seeming like it wouldn't do much for holding a bar, really builds the finger strength and the musclulature between the thumb and forefinger to help you keep your hands closed tighter against force that's trying to open it (in a way that's definitely different from using grippers). Start with three 10 lb. plates (pinching with smooth sides out), try for 4, then move to 25 lb. plates and shoot for 35s or more as you get stronger (45s are for top-level grip strength masters, I came close with 85 lbs. but never quite could get a pair of 45s off the ground).
3. Practice static holds with a barbell at the end of your workout. Load up a set weight, say, 315 lbs. on a in the power rack with just an inch or two of movement to where you'd be standing fully erect with the bar in front of your body (basically, you want to stand up an inch or two and be in the position of a deadlift lockout or the start of a shrug position). Just hold for time, start with a goal such as 3 sets of holds for 30 seconds, when you reach it, either add time (such as, 5 seconds per session) or add weight. Nothing helps you hold on to weight like.....well....holding on to weight!
Those three things will be the biggest factors to increasing grip strength for traditional lifts. Most of the other "toys" are fun to test against and work to improve on, but won't do a lot to help with everyday training. Grippers are a prime example, fun to play with (I've got about a dozen various ones stockpiled from my days of doing tons of grip work), but don't really do a whole lot for general hand strength to hold on to something heavy.