Kristi, Thank You for a great Horo thread. Spice & Wolf is based not on manga, but on a set of illustrated light novels. While there is a 2nd season of Spice & Wolf coming, those who want to review the first season in book novel form can visit the book translations at:
http://www.baka-tsuki.net/project/index.php?title=Spice_%26_WolfJust be careful not to read too far ahead and spoil the 2nd season anime.