This one is actually quite easy for me: Iron Crown Enterprise’s Middle Earth from the 1980s.
Man, did we play the shit out of those supplements. We didn’t use the Rolemaster rules or the later MERP. It was all D&D all the time back then, but damn did we love those ICE supplement with their gorgeous maps and amazing story hooks. Our campaign was 100 years after the War of the Ring, and was tied both to some resurgent evil and the return of the Blue Wizards from the East. Some of the setting particulars we had to change or adapt, but there was so much good stuff from the two Mirkwood books, the Mines of Moria, the Riders of Rohan, and so many others.
The one I remember as being the most awesome was the Court of Ardor. It had almost no connection to Tolkien’s actual stuff, but it fit really well with what we were doing in the setting.
This is me getting all nostalgic.
#RPGaDAY2015 is the brainchild of game designer Dave Chapman. Basically, each day in August there is a question about RPGs. This is day 21.