Index: src/org/openstreetmap/josm/actions/MirrorAction.java
===================================================================
--- src/org/openstreetmap/josm/actions/MirrorAction.java	(revision 0)
+++ src/org/openstreetmap/josm/actions/MirrorAction.java	(revision 0)
@@ -0,0 +1,73 @@
+// License: GPL. Copyright 2007 by Immanuel Scholz and others
+package org.openstreetmap.josm.actions;
+
+import static org.openstreetmap.josm.tools.I18n.tr;
+
+import java.awt.event.ActionEvent;
+import java.awt.event.KeyEvent;
+import java.util.Collection;
+import java.util.HashSet;
+import java.util.LinkedList;
+
+import javax.swing.JOptionPane;
+
+import org.openstreetmap.josm.Main;
+import org.openstreetmap.josm.command.Command;
+import org.openstreetmap.josm.command.ChangeCommand;
+import org.openstreetmap.josm.command.MoveCommand;
+import org.openstreetmap.josm.command.SequenceCommand;
+import org.openstreetmap.josm.data.coor.EastNorth;
+import org.openstreetmap.josm.data.osm.Node;
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.osm.Way;
+import org.openstreetmap.josm.tools.Shortcut;
+
+/**
+ * Mirror the selected nodes or ways along the vertical axis
+ *
+ * Note: If a ways are selected, their nodes are mirrored
+ *
+ * @author Teemu Koskinen, based on much copy&Paste from other Actions.
+ */
+public final class MirrorAction extends JosmAction {
+
+    public MirrorAction() {
+        super(tr("Mirror"), "mirror", tr("Mirror selected nodes and ways."),
+        Shortcut.registerShortcut("tools:mirror", tr("Tool: {0}", tr("Mirror")),
+            KeyEvent.VK_M, Shortcut.GROUP_EDIT, Shortcut.SHIFT_DEFAULT), true);
+    }
+
+    public void actionPerformed(ActionEvent e) {
+        Collection<OsmPrimitive> sel = Main.ds.getSelected();
+        HashSet<Node> nodes = new HashSet<Node>();
+
+        for (OsmPrimitive osm : sel) {
+            if (osm instanceof Node) {
+                nodes.add((Node)osm);
+            } else if (osm instanceof Way) {
+                nodes.addAll(((Way)osm).nodes);
+            }
+        }
+
+        if (nodes.size() == 0) {
+            JOptionPane.showMessageDialog(Main.parent, tr("Please select at least one node or way."));
+            return;
+        }
+
+        double minEast = 200.0;
+        double maxEast = -200.0;
+        for (Node n : nodes) {
+            minEast = Math.min(minEast, n.eastNorth.east());
+            maxEast = Math.max(maxEast, n.eastNorth.east());
+        }
+        double middle = (minEast + maxEast) / 2;
+
+        Collection<Command> cmds = new LinkedList<Command>();
+
+        for (Node n : nodes)
+            cmds.add(new MoveCommand(n, 2 * (middle - n.eastNorth.east()), 0.0));
+
+        Main.main.undoRedo.add(new SequenceCommand(tr("Mirror"), cmds));
+        Main.map.repaint();
+    }
+}
Index: src/org/openstreetmap/josm/gui/MainMenu.java
===================================================================
--- src/org/openstreetmap/josm/gui/MainMenu.java	(revision 1627)
+++ src/org/openstreetmap/josm/gui/MainMenu.java	(working copy)
@@ -41,6 +41,7 @@
 import org.openstreetmap.josm.actions.JoinNodeWayAction;
 import org.openstreetmap.josm.actions.JosmAction;
 import org.openstreetmap.josm.actions.MergeNodesAction;
+import org.openstreetmap.josm.actions.MirrorAction;
 import org.openstreetmap.josm.actions.NewAction;
 import org.openstreetmap.josm.actions.OpenFileAction;
 import org.openstreetmap.josm.actions.OpenLocationAction;
@@ -120,6 +121,7 @@
     public final JosmAction alignInLine = new AlignInLineAction();
     public final JosmAction distribute = new DistributeAction();
     public final JosmAction ortho = new OrthogonalizeAction();
+    public final JosmAction mirror = new MirrorAction();
     public final AddNodeAction addnode = new AddNodeAction();
     public final JosmAction createCircle = new CreateCircleAction();
     public final JosmAction mergeNodes = new MergeNodesAction();
@@ -269,6 +271,7 @@
         add(toolsMenu, alignInLine);
         add(toolsMenu, distribute);
         add(toolsMenu, ortho);
+        add(toolsMenu, mirror);
         toolsMenu.addSeparator();
         add(toolsMenu, addnode);
         add(toolsMenu, createCircle);