I 've used wires. I wrapped the wires (only the part that goes into the cake) with scotch tape. I got mine from a home improvement store in the electrical section. It was all coiled up and comes wrapped in hard plastic. 
I wrap or insert in a straw/hollow coffee stirer primarily so that there won't be any possible discoloration of the cake around the wire--especially if the cake is white or yellow.
Rae
I have only used wire once and I used floral wire. I didn't wrap it, but I did use a piece of hollow plastic and inserted it in the cake and then inserted the wire into the plastic. That way it didn't come in contact with the cake at all. You could also use a straw.
I tried to use a straw the first time, but it was not large enough to hold the number of wires I had. But they are a great idea for a smaller amount. The plastic tube I used was actually the leg off of a separator plate set that I had used in my Wilton course 3 cake.
Yes they have in lengths pre cut. You can just cut them down. I have heard one person say that they had rust with wire. I have not heard anything since. Have you ever seen cakes done by Sylvia or Ron Ben--The have thousands of sugar flowers and I have seen a many program where they just stick it right in the cake. It is considered a physical hazard.
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