Force the end credits on an unsuspecting player.

ForceEnd.java

package com.comphenix.example;

import net.minecraft.server.v1_4_R1.EntityPlayer;
import net.minecraft.server.v1_4_R1.Packet70Bed;

import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.craftbukkit.v1_4_R1.entity.CraftPlayer;
import org.bukkit.entity.Player;
import org.bukkit.event.Listener;
import org.bukkit.plugin.java.JavaPlugin;

public class ForceEnd extends JavaPlugin implements Listener {
    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (sender instanceof Player) {
            displayCredits((Player) sender);
        } else {
            sender.sendMessage(ChatColor.RED + "Must be a player.");
        }
        
        return true;
    }
    
    private void displayCredits(Player player) {
        CraftPlayer craft = (CraftPlayer) player;
        EntityPlayer nms = craft.getHandle();
        
        nms.viewingCredits = true;
        nms.playerConnection.sendPacket(new Packet70Bed(4, 0));
    }
}

Updated for 1.8: https://gist.github.com/Zeryther/95b7212dcbdfc4e818c6