EDIT: Lies, all lies! Don't believe any of it! Happy April Fools!

Perhaps the greatest Axis intelligence victory was using a specially equipped U Boat to tap one of the trans Atlantic telephone cables between Canada and Europe.

By hovering over the cable, and using extremely sensitive instruments to pick up the inductance of the cable, the Nazis, were able to listen in on traffic. Their most notable score was recording a conversation between Winston Churchill and President Roosevelt. From this, the Germans were able to disrupt several convoys carrying much needed supplies of spam and sewing thread to England. This actually set the invasion of Normandy back by at least two months, due to lack of rations.

If you can find a copy of the May 1985 Journal of Telecommunications, you'll find a well written article on Operation Wiretap.

I would say the way the Germans managed to hide their intentions prior to the Battle of the Bulge in late 1944 qualifies here. I'm afraid I don't have the book I'm using as my source because I'm not at home, so this is from memory. I hope that's okay. I'll see if I can find the name of the book so others can corroborate this.

First of all, Hitler, for once, actually had a good idea and named the plan "Wacht am Rhein" (Watch on the Rhine). This defensive sounding name was deliberately chosen to appear nonthreatening if allied intelligence picked up any snippets about it.

Secondly, they avoided using Enigma-coded messages despite continuing to have confidence the allies had not cracked it. The allies had become maybe slightly too reliant on Enigma intercepts, so this definitely contributed to the total surprise the Germans achieved on December 16th. The Germans also avoided using radio, possible with their own extensive telegraph network.

The German buildup was well concealed from allied reconnaissance flights. Troop movements predominantly occurred at night, and they again managed to make them look defensive, as though they were anticipating an allied assault on Aachen to the north of the Ardennes, before moving to their actual staging areas shortly before the assault. It is worth mentioning that allied planners could have looked at a map and seen that the rail lines the Germans were using extended to right opposite the Ardennes. In the days leading up to the 16th, German infantry units slowly advanced to within a couple of kilometres from the allied front, maintaining strict discipline with regards to light and noise.

Whilst of course the military aim of reaching Antwerp was never realistically a possibility, the political aim of the German plan (to fracture the UK-US relationship) came worryingly closer. Eisenhower was very close to firing Field Marshal Montgomery after he criticised US strategy and demanded control of all allied forces on the western front. Only a sincere last-minute apology from Monty got him off the hook.

So not really an intelligence victory on the scale of allied deceptions prior to D-Day, but they still managed to achieve complete surprise.

Edit: source is this book http://www.ospreypublishing.com/store/Ardennes-1944_9780850459593