Oh wow... picking favorites is impossible!
If I were to choose, I'd break them into three categories. Rifles, awards/medals, and helmets.
1. Rifles - Carcano 91/28 Special Troop carbine. It is in amazing shape and the barrel was made by Beretta (yes, THAT Beretta) in 1932. I posted pictures of it and experts were stumped by the markings on it, specfically a "K" stamping. It turns out that "K" stands for Krupp, and it's a marking you just NEVER see on Carcano rifles. The steel used for the barrel was made by the famous Krupp in Germany prior to 1914. As Germany and Italy were on opposing sides during WWI, the shipment of steel which would later become the barrel on my rifle was withheld. In 1932, the Krupp steel arrived in Italy and was made into barrels by Beretta. The barrel of my rifle was born... In that same year, Beretta sent the barrel to the arsenal at Terni, and it was mated to a Terni receiver. To round it off, my future wife bought this rifle for me this past Valentine's Day.
IBM M1 Carbine. My M1 Carbine is the first rifle in my collection. The receiver and barrel were made by International Business Machines (Now IBM computers) in Poughkeepsie, NY in 1943. It saw use in WW2, Korea, and possibly later conflicts like Vietnam. A stamping on the stock also tells me that it was used by the Israeli Defense Force. I decided to buy this rifle because of the local history behind it... I live in Hyde Park, NY (hometown of President F.D.R.) and the IBM factory that made my rifle stood about 5mins south on Rt. 9 from my house! I do believe that the building where my carbine was built was demolished after the war, but on the same property, IBM has a massive plant where they build microchips and other computer components.
War Merit Cross 2nd Class. I won this medal in the WRF holiday raffle. Special thanks to Bond for donating the medal, and Ade for organizing the raffle! It will become a center piece to the collection of medals I share with my history students!
Orders of the Red Star. I've been able to find a few of these for cheap on ebay. I think it's amazing that you can fully research them based on the serial number on the back. You can find out what the individual soldier did to be awarded it, and get the service record for the soldier which will tell you what he or she did during the entire course of the war! Better yet, if the Red Star was awarded to an officer, his/her service record almost always includes a picture of the soldier! To top it all off, my grandfather on my mother's side was in the Red Army... so that's why I find this stuff interesting. Two of my Red Stars have been researched. One belonged to a supply officer who did an excellent job in making sure artillery was well fed. The second belonged to a front-line political commisar. The more I read about commisars, I'm finding that they really were amazing individuals! They were equal parts combat soldier, care taker for their men, and proponent of communism.
Helmets. Both the M35 Heer and Type 90 Japanese helmets were given to me by customers at the recycling facility my family owns.
The Japanese lid was given to me by a customer named Anthony. His father-in-law, George J. Ritz served in the U.S. Navy as a coxwain on Landing Ship Medium 264 which participated in the Iwo Jima operation. G.J. Ritz brought this helmet home as a souvenir from Iwo Jima. It sat in his attic pretty much from 1946 until it was given to me this past summer. G.J. Ritz passed away, and nobody left in his family really appreciated it, so Anthony was very pleased to give it to me to show to my high school history students. This helmet is in amazing condition, although the leather liner is fragile because of the extreme high and low temperatures it was exposed to in that attic... To top it all off, I have tons of documentation and G.J. Ritz's medal grouping which proves that this helmet was taken from Iwo. I also have some personal photos that were snapped on LSM 264 while it was in Pearl Harbor.
The German lid was bought by a customer named Clyde at an antique store. He wanted to paint it up and wear it on his Harley... LUCKILY, he never got around to it and it had been sitting in his closet for a few decades collecting dust. He saw a sign I posted and just gave it to me!