Added pre-login event for catching logins right after name verification has completed. This happens in a different thread from the server (and thus can also block).

src/main/java/org/bukkit/event/Event.java

@@ -152,6 +152,13 @@ public abstract class Event implements Serializable {
          */
         PLAYER_LOGIN (Category.PLAYER),
 
+        /**
+         * Called when a player has just been authenticated
+         *
+         * @see org.bukkit.event.player.PlayerPreLoginEvent
+         */
+        PLAYER_PRELOGIN (Category.PLAYER),
+
         /**
          * Called when a player respawns
          *

src/main/java/org/bukkit/event/player/PlayerListener.java

@@ -100,6 +100,14 @@ public class PlayerListener implements Listener {
     public void onPlayerLogin(PlayerLoginEvent event) {
     }
 
+    /**
+     * Called when a player has just been authenticated
+     *
+     * @param event Relevant event details
+     */
+    public void onPlayerPreLogin(PlayerPreLoginEvent event) {
+    }
+
     /**
      * Called when a player throws an egg and it might hatch
      *

src/main/java/org/bukkit/event/player/PlayerPreLoginEvent.java

@@ -0,0 +1,126 @@
+
+package org.bukkit.event.player;
+
+import java.net.InetAddress;
+import org.bukkit.event.Event;
+
+/**
+ * Stores details for players attempting to log in
+ */
+public class PlayerPreLoginEvent extends Event {
+    private Result result;
+    private String message;
+    private String name;
+    private InetAddress ipAddress;
+
+    public PlayerPreLoginEvent(String name, InetAddress ipAddress) {
+        super(Type.PLAYER_PRELOGIN);
+        this.result = Result.ALLOWED;
+        this.message = "";
+        this.name = name;
+        this.ipAddress = ipAddress;
+    }
+
+    /**
+     * Gets the current result of the login, as an enum
+     *
+     * @return Current Result of the login
+     */
+    public Result getResult() {
+        return result;
+    }
+
+    /**
+     * Sets the new result of the login, as an enum
+     *
+     * @param result New result to set
+     */
+    public void setResult(final Result result) {
+        this.result = result;
+    }
+
+    /**
+     * Gets the current kick message that will be used if getResult() != Result.ALLOWED
+     *
+     * @return Current kick message
+     */
+    public String getKickMessage() {
+        return message;
+    }
+
+    /**
+     * Sets the kick message to display if getResult() != Result.ALLOWED
+     *
+     * @param message New kick message
+     */
+    public void setKickMessage(final String message) {
+        this.message = message;
+    }
+
+    /**
+     * Allows the player to log in
+     */
+    public void allow() {
+        result = Result.ALLOWED;
+        message = "";
+    }
+
+    /**
+     * Disallows the player from logging in, with the given reason
+     *
+     * @param result New result for disallowing the player
+     * @param message Kick message to display to the user
+     */
+    public void disallow(final Result result, final String message) {
+        this.result = result;
+        this.message = message;
+    }
+    
+    /**
+     * Gets the player name.
+     * 
+     * @return
+     */
+    public String getName() {
+        return name;
+    }
+    
+    /**
+     * Gets the player IP address.
+     * 
+     * @return
+     */
+    public InetAddress getAddress() {
+        return ipAddress;
+    }
+
+    /**
+     * Basic kick reasons for communicating to plugins
+     */
+    public enum Result {
+        /**
+         * The player is allowed to log in
+         */
+        ALLOWED,
+
+        /**
+         * The player is not allowed to log in, due to the server being full
+         */
+        KICK_FULL,
+
+        /**
+         * The player is not allowed to log in, due to them being banned
+         */
+        KICK_BANNED,
+        
+        /**
+         * The player is not allowed to log in, due to them not being on the white list
+         */
+        KICK_WHITELIST,
+        
+        /**
+         * The player is not allowed to log in, for reasons undefined
+         */
+        KICK_OTHER
+    }
+}

src/main/java/org/bukkit/plugin/SimplePluginManager.java

@@ -75,10 +75,12 @@ public final class SimplePluginManager implements PluginManager {
 
         Pattern[] patterns = instance.getPluginFileFilters();
 
+        synchronized (this) {
             for (Pattern pattern : patterns) {
                 fileAssociations.put(pattern, instance);
             }
         }
+    }
 
     /**
      * Loads the plugins contained within the specified directory
@@ -145,7 +147,7 @@ public final class SimplePluginManager implements PluginManager {
      * @throws InvalidPluginException Thrown when the specified file is not a valid plugin
      * @throws InvalidDescriptionException Thrown when the specified file contains an invalid description
      */
-    public Plugin loadPlugin(File file) throws InvalidPluginException, InvalidDescriptionException, UnknownDependencyException {
+    public synchronized Plugin loadPlugin(File file) throws InvalidPluginException, InvalidDescriptionException, UnknownDependencyException {
         Set<Pattern> filters = fileAssociations.keySet();
         Plugin result = null;
 
@@ -175,11 +177,11 @@ public final class SimplePluginManager implements PluginManager {
      * @param name Name of the plugin to check
      * @return Plugin if it exists, otherwise null
      */
-    public Plugin getPlugin(String name) {
+    public synchronized Plugin getPlugin(String name) {
         return lookupNames.get(name);
     }
 
-    public Plugin[] getPlugins() {
+    public synchronized Plugin[] getPlugins() {
         return plugins.toArray(new Plugin[0]);
     }
 
@@ -246,7 +248,7 @@ public final class SimplePluginManager implements PluginManager {
      * @param type Type of player related event to call
      * @param event Event details
      */
-    public void callEvent(Event event) {
+    public synchronized void callEvent(Event event) {
         SortedSet<RegisteredListener> eventListeners = listeners.get(event.getType());
 
         if (eventListeners != null) {

src/main/java/org/bukkit/plugin/java/JavaPluginLoader.java

@@ -258,6 +258,12 @@ public final class JavaPluginLoader implements PluginLoader {
                     ((PlayerListener) listener).onPlayerLogin((PlayerLoginEvent) event);
                 }
             };
+        case PLAYER_PRELOGIN:
+            return new EventExecutor() {
+                public void execute(Listener listener, Event event) {
+                    ((PlayerListener) listener).onPlayerPreLogin((PlayerPreLoginEvent) event);
+                }
+            };
         case PLAYER_EGG_THROW:
             return new EventExecutor() {
                 public void execute(Listener listener, Event event) {