Might as well begin with the grandaddy of them all. Hardware Wars from 1978.
https://youtu.be/cGDdFuDwTZ8
Director Ernie Fosselius later worked in the sound dept. on Return of The Jedi and Spaceballs.

And the one that really got the fan film ball rolling in 1997. Troops
https://youtu.be/-EDiQXhYIKY
Youtube didn’t even exist when this was unleashed on an unsuspecting internet.
With it’s unique take on events that happened offscreen in the original film, Rogue One probably owes this one a debt. 😉
Director Kevin Rubio has gone on to write some of the funniest Star Wars comics ever. (Among other things.) Wish he could make one of the spinoff movies.

I.M.P.S. The Relentless
https://youtu.be/bHJkxEVENPI
Picking up where Troops leaves off, this is a semi documentary look at the brave soldiers of the Empire.