I run 2 setups on cordless that I have standardized on: Bosch compact 12V and Makita 18V -both Li-ion types. The small Bosch stuff is awesome for lighter work. Their 12v driver (with a hex collet) is my preferred screw driver for anything #8 and smaller and less than 2". Superb control, fits anywhere and can be brought along in your tool belt easily. For electrical work (other than boring large holes) it is da bomb. i set the clutch and can consistently torque down breaker contacts and connections on switches and outlets, etc. Finish cabinet work too. I also have a mini drill/driver with a regular chuck and a 90deg adjustable driver that can fit anywhere.
For the big stuff, the makita 18V is pretty darn solid. Impact drivers are the best thing for driving screws, lags, you name it. Grab one of those 5" long RSS screws and a torx bit, and watch it melt right into an LVL with a good impact driver. I find a lot of use for the small circ saw, an occasional use for the sawzall and grinder and flashlight. The caution is the sawzall and grinder will suck a battery dry is a minute, flat out. Since I got my set they have come out with larger AH batteries (mine are 2 AH) so those would help, but they are also bigger and heavier. A lot of this all depends on what you are doing, so YMMV.
At this point in time, you want to cut loose from niCad or NiMH battery technologies and move into Li for sure. Like several others have said.