Terry is right. "It really depends on what he needs it for."
12v is for medium jobs around the house. An 18v is certainly for very heavy jobs but unless he has strong hands, this size is very bulky. If I can add my $.02, I've found that the 14.4v Cordless is good for work around the home. It will certainly drive deck screws and screws into oak for a while but you will change the battery out after an hour or so. For me, that's no problem because the 14.4v has a quick charge. (I got a DeWalt, who is owned by Black & Decker now, with 2 batteries. While I'm using one, the other is on the charger. DON'T leave the battery on the charger too long. It can get ruined along with the charger. (I did this!)
Yes, Home Depot carries a lot of the brand names as does Sears. It wouldn't hurt to talk to some of his 'pals' to see if they have a Cordless (and Corded) drill. Maybe your husband has mentioned to them of a particular one that he wants. Happy Holidays!