What's your favorite plugin, and why? It can't be your own.. Mine is Commandbook - reason being it's simplicity and I <3 sk89q.
Worldedit. I make so many servers, and I HATEHATEHATE minecraft ore generation, so I generate my own with %'s via worldedit
mcMMO, as it brings much much more fun to servers, and brings that RPG feel to Minecraft, and can have an infinite amount of things added to it.
Yes and no, Double 0, we make the worlds with WorldPainter, and we make ore "deposits" in x area with x percentages. Works out great, people always love it.
World guard, its a life saver. I also like Double0negative survival games, and bukkit games. Theres just too many good plugins out there