Shows your Bukkit server to the LAN

LanBukkit.java

package com.md_5;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.util.logging.Level;
import org.bukkit.plugin.java.JavaPlugin;

public class LanBukkit extends JavaPlugin implements Runnable {

    private DatagramSocket socket;
    private InetSocketAddress broadcastAddr = new InetSocketAddress("224.0.2.60", 4445);

    @Override
    public void onEnable() {
        try {
            socket = new DatagramSocket();
            getServer().getScheduler().scheduleAsyncRepeatingTask(this, this, 0, 30);
        } catch (IOException ex) {
            getLogger().severe("Could not start LAN server broadcaster");
        }
    }

    @Override
    public void onDisable() {
        if (socket != null) {
            socket.close();
        }
        getServer().getScheduler().cancelTasks(this);
    }

    public void run() {
        try {
            byte[] broadcast = ("[MOTD]" + getServer().getMotd() + "[/MOTD][AD]" + getServer().getIp() + ":" + getServer().getPort() + "[/AD]").getBytes();
            socket.send(new DatagramPacket(broadcast, broadcast.length, broadcastAddr));
        } catch (IOException ex) {
            getLogger().log(Level.SEVERE, "Caught exception, shutting down", ex);
        }
    }
}

That's what Minecraft itself uses pretty much and what I use in my slightly modified version, but thanks again.

For certain linux machines, InetAddress.getLocalHost() does not work and generates an error. For my implementation, I just put a question mark (or other invalid host name), and it works correctly to get the IP address.
Also, line 13 should have a broadcast IP address, I just use 255.255.255.255 for simplicity (for some reason I was unable to get broadcasts without it...).
Other than that, it seems to work flawlessly!