The following are some concepts for campaigns set on Tolkien's Middle Earth that I came up with. Naturally, they are guided by my readings and tastes. I have not read most of Tolkien's writings outside of The Hobbit and The Lord of the Rings, but I know that others in my group had. Thus, I wanted to set my campaign in roughly the same period and regions there -- perhaps a decade or two before The Hobbit or after Lord of the Rings -- and perhaps ranging into neighboring countries than those covered, but not by much.
This is an alternate storyline set in Rohan shortly after The Hobbit and prior to Lord of the Rings. Some in Rohan are lead to suspect treachery of Saruman. They have no proof, however, and undertake to root out his evil.
An alternate storyline where Galadriel accepts the One Ring when Frodo offers it to her. She avoids using it, and plans to help Gondor and Rohan fight to make a safe passage to Mount Doom so that it can be destroyed. However, this is fraught with peril on both sides. The campaign begins as the forces are close to taking the fight into Mordor itself.
Prior to Lord of the Rings, a company in Bree are recruited to help root out the remnants of the Necromancer's rule in Mirkwood -- leading to various adventures along the way.
A hobbit-centric alternate storyline where Frodo is forced to hide the Ring when the black riders come on him in the Shire, and he disappears. In the months that follow, dark forces swirl around the Shire as forces are drawn there.