I'll try to mention things not mentioned before...
I have seen photos M4A3 with Iron Crosses, I think they were used for evaluation or training. There might have been a second line unit or two that had them.
There were 3 non-Russian tanks the Germans liked and used. The first 2 were French the Char-B bis and the S-35 Samoa. Both of these were superior to anything the Germans had in 1940 and were studied extensively. The Char-B was the first Heavy Tank used in WWII and it inspired the Tiger Tank. 161 Char were captured during the fall of France. The S35 was also used during WWII by the Italians and by the Germans and Vichy in West Africa.
The last tank I will mention, is the the Pz-38(t). Although the tank itself was obsolete, the chassis was a automotive masterpiece. German enginners captured several, removed the turret and fashioned a fixed turret with good sloping armour and a high velocity 75mm they could destroy any Allied tank except the Russian Super-Heavys. It was fast, menueverable, reliable, and was very difficult to destroy due to its small size. This became the German Jadspanther 38 Hetzer.
I will mention one weapon the Germans loved was the Russian PPsh-41. They tried to grab as many as they could and even figured out a simple field modification for it to fire German 9mm Parabellum rounds.
The Germans did have a respect for the American rifles, but they didnt use them that much because there own Gewehr 41 and 43 were starting to become available not to mention the fancier guns such as the Fg.42 and Stg.43/44. Also after 1940, The Germans had a clear preference for SMGs than rifles and tried to equip their units with them as opposed to rifles. This was espically true of the SS and Panzergrendier units.