Due to legal issues, all downloads from Spigot and Bukkit are down.
If you need Bukkit or Spigot, here you can download the latest Spigot releases, compatible with Minecraft 1.8! I couldn’t find a Bukkit.jar but Spigot is fully compatible with Bukkit’s plugins and a lot better.
Also, Spigot has iniciated a new update mechanism using patches: YOU have to generate the update using the Spigot #1649 Build that you can download here and the latest patch from spigotmc.org.
The download’s md5 checksum is the same as the original download from spigotmc.org.
Let’s hope that Bukkit and Spigot will be online again soon or we’ll maybe have to search another server solution 😉