Let's start immediately with my personal top 5 of plugins for a Bukkit server.
5. On number 5, we have Multiworld. This plugin allows the admin to add more than 1 Minecraft world to his server. Easy comments and good world generation makes it fun for the admins and players to make and explore new worlds.
Download: http://dev.bukkit.org/bukkit-plugins/multiworld-v-2-0/
4. As number 4, I chose Essentials. Essentials is the best plugin if you need an easy and simple warp system. The plugin also allows to use funny commands like /ping or /kittycannon. It's eady to install and used on almost every Bukkit server.
Download: http://dev.bukkit.org/bukkit-plugins/essentials/
3. Number 3 is a quite handy one, WorldEdit. With WorldEdit you can fill in area's with certain block types. Commands are clear and tools can be used to do it as well. WorldEdit is also one of the most used plugins. The ability to create spheres or cubes without touching your mouse amazes me and many other people.
Download: http://dev.bukkit.org/bukkit-plugins/worldedit/
2. A deserved 2nd place is for Factions. With this plugin players can join a faction and fight other factions. Each faction can claim its own land. This plugin is always very funny if you want to make a kingdom like server.
Download: http://dev.bukkit.org/bukkit-plugins/factions/
1. And finally on the 1st place is... MoveCraft! MoveCraft allows the player to create moving vehicles in Minecraft. These vehicles may be a bit slow, but they're still amazing. The serverowner can also add customized vehicles to the plugin. Combined with factions, this can lead to awesome wars with tanks and planes.
Download: http://dev.bukkit.org/bukkit-plugins/movecraft/

So that was my top 5 of Bukkit plugins, I hope you enjoyed it and subscribe!
I did NOT make all the plugins myself. If you want to know who made these awesome plugins, click on the download link under every number!