The Antares is unusual in that it's using solid-fuel in the second stage. I was surprised about that and a couple of questions immediately popped up which are already covered on this site: How can a solid-fuel stage control thrust and what are the advantages of using a solid-fuel upper-stage (no answers to that question at the time of this writing).
Since using a solid-fuel upper stage is unusual in a rocket that can achieve orbit, I was wondering whether there are other rockets besides the Antares that have used or are using this design?