Actually, in spite of my earlier reply, I'd go for the traditional method.
A computerised system is all well and good but many people are suspicious about the visibility and accounatbility of the software, (and the geekiness of someone who tries to use one for such a purpose
) and you're bound to have someone who'll point out that a computer is not a true random number generator and never can be.
Plus, if the technology lets you down (chances = fair to middling) you look like a right trumpet on the big night!
Tickets, big barrel, girly to pull them out*.
(*And the tickets too)