What do y'all recommend for improving grip strength with an open grip? All of the grip exercises I've heard of involve having your hand closed or nearly closed, but when I lose my grip while bouldering due to lack of grip strength, it's always when my hand is almost all the way open.
Are you bouldering in a gym, or outside? A good gym should have a grip board set up, which has all the different holds on it... jugs, one/two/three finger pockets, slopers, and bear claws. Couple minutes a day just hanging from them will do the trick... my routine was something like 45 seconds on the jugs, 3x5 seconds in the 3 finger pockets, 3x10 seconds on the sloper. Do three sets of that a few times a week, and your grip strength goes through the roof... starting out is a huge challenge though.
A campus board is also good for building arm/back strength... just a board with small wooden handles, to travel up and down on.
If you don't have any of those, the easiest thing to do is just to stay on the wall for extended periods of time, without getting off... say, 15 minutes at a time, just moving back and forth, finding new resting positions, practicing movements, etc etc etc.
As far as gym exercises, to increase your pinch grip strength, just pick up a smooth plate (ie, not on the handle) in each hand, and hold it as long as possible. Other exercises I'd recommend are wrist curls, preacher curls, and upright rows... it's all in your forearms.
If you're just starting, you'll be forced off the wall with pumped forearms for a few months before you get used to it... it definately takes some patience.