I'm kind of surprised no one has mentioned Gracie Screwdrivers, they used to sell them for different applications and are the finest screwdrivers I have ever used on all my firearms. I have picked them up whenever the opportunity presents itself and modify them to fit a particular need. I have a stubby that fits in my shooting box that gets used the most to remove side plate screws providing access to blackpowder rifle locks for cleaning. I have a set that is always with me at the range, they all fit in a cigar box and I guard them from jealous borrowers (who I trust)
My first set of gun screw drivers I got from Chapman's, they have a set of bits with a neat ratchet and screwdriver handle as well as an extension. They are also available on-line and come in different sets, along with allen heads, and hex head bits.
A friend of mine showed off his new screwdriver set he got on the internet, it is a square tube that encloses a crazy set of miniature bits in every persuasion along with an electric driver with two different torque settings, perfect for everything from eyeglasses to fine scope, target sight screws, damn thing even has a light and comes with a charger.