What do you have?

I've got a couple of cordless drills, a corded drill, a drill press, 2 old yankee screwdrivers, an eggbeater drill, and 3 antique braces w/bits. Now assuming you don't suffer from the same strange compulsion to buy tools I do, I'd have to say any of the good brands of cordless drill drivers are good. I'd suggest either 12 or 14.4 volts, and if you can swing the money, lithium ion (li-ion) over nickel cadmium (ni-cad). That said, I have a Dewalt 12 volt ni-cad (5 years old, w/rebuilt batteries) and a 12 volt Milwaukee li-ion. I use both the Dewalt and the Milwaukee on most projects, especially where I'm using pocket screws. I set the ni-cad to drill, and the Milwaukee to screw the pocket screws. I'm actually now looking to buy an impact driver.....at least until my wife finds out.

I would recommend new here, instead of used, because the batteries are the most expensive part, and you want to have the comfort of the warranty if the batteries are bad. Buying used, you have no idea what kind of shape the batteries are in, and could easily spend more on a used kit if you have to replace a battery than if you bought new. Brands are a personal preference thing, practiically all of the mid-range priced stuff at blue or orange are just fine. I personally haven't had much luck w/Black and Decker, and tend to buy some of the higher end tools simply because I use them a lot, and it's cheaper for me to spend the money once, rather than to replace a tool after a couple of years of use. If all you are doing is just some stuff here, and maybe a little home repair/hanging pictures type stuff, then the mid-range brands will do you just fine. 

Joe

We have a DeWalt that we really like. I'd recommend getting two batteries (so that you can swap them in the middle of a project) if you can afford it. I'd also recommend getting Forstner (spelling?) bits for drilling holes that need to be perfect (think holes for adjustable shelving), but I'd maybe buy them individually in the sizes you think you'll use most frequently (i.e. 1/4"). You can buy "sets" of the corkscrew-type drill bits you'll use most often. I guess I don't know what a screw gun is–we just use our cordless drill for screwing things in, you can dial the speed and torque up/down on the DeWalt's depending on your project, but I'm sure that other brands have a similar feature.

I have a hammer, a screwdriver, and a flexible fabric measure (like the kind you use for sewing)!!