I find magazines are a great thing to get someone if you don't know what to get them. Buy a subscription to a magazine that has something they are interested in - and buy him one hands on magazine - put it in a shirt nix and that way he has something to buy that day
To select a birthday gift for your Father, think of the things he enjoys. If he loves western movies, get him a western DVD. If he's into fishing, some new lures would be great. If he's a handyman, how about a new level or stud finder.