Brownell's sells an interchangeable bit screwdriver set under the name Magna Tip.

I have had The Magna Tip Super set in my shop for over 25 years. They have a wide range of bits to fit about any screw you might encounter.

By the way if you break one of their bits send it in and they will replace it free of charge. Bits do break and I save the broken ones for grinding specialty bits.

http://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=417&title=MAGNA-TIP%20SUPER%20SETS?