We always hear about the tiger tank and how formidable it was, as well as other Nazi weapons like the rockets. Did the allies have weapons that struck the same fear on the axis?
Allied close air support generally struck the same type of fear into the Nazi ground forces after the Normandy invasions. By that time, the Allied air forces had nearly complete control over the skies. Furthermore, the Allies always had fighter-bombers loitering over the front waiting to get a call to attack German positions. The Germans came to be terrified of the Thunderbolts and Typhoons for their tenacious and accurate strikes.
A good book to read on this sort of thing is Hell Hawks! by Robert Door. It follows a P-47 squadron through the war and gives very detailed narratives of their ground strikes and missions.
Another decent read is Zemke's Wolfpack. This one might not be printed any more as I got it probably 20 years ago, but it is about the 56th FG, who escorted bombers, strafed ground targets, bombed ground targets, and basically did everything.
The Soviet Katyusha Artillery was effectively the horror of many German soldiers on the Eastern Front. One of the first Rocket Artilleries of the war, the Soviet employed the Katyusha extensively with their signature, massive artillery bombardments that always preluded their attacks and offensives. The effect that the Katyusha had on German morale and willpower was incredibly demoralizing. Due to the shrieking and terrifying sound that they produced, and the sheer amount of death and destruction they would be able to inflict, many German soldiers were simply shattered by how brutal they were. Combined with conventional howitzer artillery, Katyushas could make artillery bombardments last for minutes, during which many Germans would lose their nerve. Just for perspective, though they were somewhat inaccurate, a proper salvo from 4 Katyusha's could produce the equivalent destruction of 72 guns.
The T-34 was also a feared tank to a reasonable degree before the arrival of the Tiger tanks and the Panther. The Panzer III and Panzer IV just weren't powerful enough to defeat the T-34, and had to charge T-34's and fire point blank at times to actually destroy them. The T-34 was the Soviet equivalent of the Tiger between 1941 and early 1942, until the Germans found a sustainable and efficient way of dealing with them.
Also, like the_8th-henry mentioned, Allied air power was effectively the bain of the German army towards the end of the war as the Luftwaffe disintegrated. Notable Generals, like Erwin Rommel, respected the sheer strength of the Allied airforces. On both of the fronts, once the Luftwaffe's role was mitigated, Allied airpower became demoralizing to the German troops, who seemed to be bombed and hurried by planes constantly without any aid of their own.
The Pentagon had decided it was too dangerous to have a fuze fall into German hands because they might reverse engineer it and create a weapon that would destroy the Allied bombers, or at least find a way to jam the radio signals. The Pentagon refused to allow the Allied field artillery use of the fuzes in 1944, although the United States Navy fired proximity-fuzed anti-aircraft shells during the July 1943 invasion of Sicily.[22] After General Dwight D. Eisenhower demanded he be allowed to use the fuzes, the VT fuzes were used in the Battle of the Bulge in December 1944, when they made the Allied artillery far more devastating, as all the shells now exploded just before hitting the ground. It decimated German divisions caught in the open. The Germans felt safe from timed fire because they thought that the bad weather would prevent accurate observation. The effectiveness of the new VT fused shells exploding in mid-air, on exposed personnel, caused a minor mutiny when German soldiers started refusing orders to move out of their bunkers during an artillery attack. U.S. General George S. Patton said that the introduction of the proximity fuze required a full revision of the tactics of land warfare.
Allied air power, especially towards the end of World War 2 was especially fearsome to the Germans. The RAF and USAF built very capable four engine long ranged bombers, particularly the Lancaster and the B-17 Flying Fortress. Allied fighters were also formidable. After the Battle of Britain the RAF Spitfire became a household name. Though the Germans had excellent fighters with the Messerschmitt 109 and the Folk Wolf 190, air wars over France soon gave way to the RAF. During the Normandy invasion in 1944 the skies belonged to the allies. When the USAF came in 1942, with the longer range P-51 Mustang and devastating P-47 Thunderbolt, along with the Spitfires, the allies gained air dominance near the end of the war. Even the Messerschmitt 262 jet could not stop the allied air force. Despite its incredible speed, allied fighters were still able to take it down with Mustangs and Spitfires. In the end, it was the bombers, 1000 planes a night, decimating cities like Dresden, that wrought fear into the Germans.
Did the allies have weapons that struck the same fear on the axis?
Sure - prior to the introduction of the Tiger (but more influentially, the up-gunning of the Panzer IV and StuG assault guns with a high velocity 75mm cannon) and the introduction of a new generation of infantry anti-tank weapons in mid-1942, the German tanks and AT units were decisively inferior to their opponents' heavy tanks, such as the French Char B1 bis, and the Soviet T-34 and KV models.
On numerous occasions this tactical inferiority provided serious setbacks, and even outright panic amongst German troops - who had derisively nicknamed their ubiquitous 37mm AT guns 'door-knockers' due to their almost complete uselessness against certain enemy AFVs. KH Freiser relating an encouinter with French Chars at Stonne in 1940 from The Blitzkrieg Legend:
This situation produced the first signs of panic in the elite Großdeutschland Regiment. The soldiers felt that they were powerless against these monster tanks. Most of all, they were terrified by the thought of being crushed by the tracks of these steel giants. Some infantrymen now simply took off, but the crews of the antitank guns continued to hold their positions, although the situation became increasingly hopeless.
An Red Army report about an attack by Soviet tanker Pavel Gutz from early fighting during Barbarossa:
The Germans started bombing the column… A shell from a German anti-tank gun bounced off the tank's heavy armour… Gudz, who was the tank's gunner as well as its commander, fired a single shot in return and the gun was destroyed. He and his platoon went on to knock out five German tanks, three armoured personnel carriers and several cars… After lunch the Germans attacked again. Gudz knocked out three more tanks. His driver Galkin rammed another German tank, dislodging its caterpillar track and forcing it into a ditch. The fields were covered with burned-out tanks and dead Germans.
An account by German general Erhard Rauss from Army Group North:
It was not so much the numerical superiority of the enemy which made the situation precarious for our command and troops, but the totally unexpected appearance of colossal tanks for which German tanks and anti-tank weapons appeared to be no match… Even the concentrated fire of the artillery and all other heavy weapons of the Kampfgruppe was not able to keep off the steel pachyderms. Though enveloped in fire and smoke, they immediately started attacking and crushed everything in their paths. Untroubled by the shower of heavy howitzer shells and earth falling down upon them, they attacked road block 121 in spite of the flanking fire of the anti-tank guns from the wooded areas, rolled over the anti-tank guns dug in there and broke into the artillery area. About one hundred friendly tanks, one-third of them were Panzer IVs, now assembled for a counterattack. Some of them faced the enemy in front, but the bulk made an assault from the flanks. From three sides, their shells hammered against the steel giants, but the effort to destroy them was in vain. On the other hand, very soon we had casualties ourselves.
By most/all accounts, the Germans were both immensely impressed, and often terrified by the T-34, and these traumatic tactical experiences lead directly to the design of the German heavy tanks of the late war (the Panther began life, as basically a bootleg T-34).