I've found that two carpenters make the best team for efficient cabinet installations. The task that sometimes requires extra hands, however, is lifting and holding uppers, especially if you pre-gang them on the ground. For this, a lift can quickly pay for itself in increased productivity, higher quality, and less fatigue.
Little Hand and 3rd Hand. Unlike many carpenters, I set my bases first. I then lay OSB or plywood across the tops for a work surface and pre-assemble my uppers into gangs. Then I lift the gangs to a 54-inch-high furring strip. This is where a lift like FastCap's Little Hand is, well, handy.
It works a little like a car jack with a caulk gun trigger: Squeezing the trigger extends a ram that helps hold the cabinets in place. At each end of the Little Hand is a 3-inch-by-5-inch skid-resistant plate. One plate sits on the base cabinet and the other contacts the underside of the upper box. I also found that two of them are great for raising a vanity-height desk drawer. The Little Hand extends from 14 inches to 22 inches and has a 70-pound capacity.
If you install your uppers first, use the company's 3rd Hand tool. The 3rd Hand works the same way as the Little Hand, but off the floor. It has a lift range from 4 feet to 10 feet and a 70-pound capacity. Adjust it to roughly where the bottom of your uppers lay out. Next, place it below the line and lift the cabinet to the wall, resting it on the 3rd Hand. Now, squeeze the trigger and micro-adjust the cabinet to the line. Even if the 3rd Hand isn't precisely plumb, the top and bottom plates pivot. This enables you to get the cabinet right on the line. You still have to push the box to the wall, but the 3rd Hand takes the load until you drive the first screw.
Cabinet Pro. If you set uppers first, there are lifts that both support and balance the uppers. The CabinetPro from E-Z Spread N' Lift Industries is a simple device with roller ball casters for moving a box into location. Despite its 400-pound capacity, the tool is designed to lift cabinets singly. The support post has pin stops at 4-3/8-inch intervals for gross adjustment and a turn screw with a 6-inch fine tuning range. The lift range is from 53-1/2 inches to 96 inches. Be careful using the Cabinet Pro over finished floors: Loaded with a weighty cabinet, the casters can imprint the floor. Double layers of cardboard protect against this, although you probably should be using them anyway when working over a finished surface.
GilLift. Telpro's GilLift is capable of raising 450 pounds of ganged cabinets. We use it as a workstation for cabinet assembly with a 2x12 plank as a bench top. We screw several cabinets together at a comfortable work height then roll the GilLift into position and easily raise the cabinets. This eliminates fiddling with shims when installing cabinets singly. Because we pre-gang these cabinets, the faces already are flushed out, and we only need to shim the hollows along the wall. The GilLift isn't cheap, but it's so efficient, I changed my "bases first" technique.