Here's one final September call-up for your consideration: Colorado Rockies outfielder Stephen Cardullo. He is probably the "most unlikely" late-season promotion of them all: you won't find him on any pre-season prospect lists because up until this past spring he wasn't even in affiliated baseball!
Cardullo played four seasons of college baseball at Florida State University and was successful, hitting .332/.439/.548 over four seasons. This was particularly notable because he came into college as a walk-on, not a scholarship player, and had to earn his way onto the team. Drafted in the 24th round in 2010 by the Arizona Diamondbacks, he drew his release after playing for one and a half seasons in the Pioneer League. In 2012 he played for London and Florence in the independent Frontier League, then moved on to Rockland in the independent Can Am League for 2013, 2014 and 2015.
He was very impressive in 2015, hitting .331/.410/.518 with nine homers, 23 steals, and a 49/42 BB/K in 359 at-bats. The Rockies picked him up as a free agent this past January. He was initially assigned to the Boise roster (that's short-season A-ball), but impressed the team enough in spring training that he opened '16 with Triple-A Albuquerque.
He played quite well for the Isotopes, hitting .308/.367/.522 with 17 homers, 32 walks, and 58 strikeouts in 406 at-bats while impressing Pacific Coast League observers with his combination of solid pop and good contact hitting skills. Although the home park helped (.981 OPS), he was decent on the road as well (.801). The Rockies called him up at the end of August and he's 7-for-26 (.269) with a pair of homers so far.
Cardullo is 6-0, 215, a right-handed hitter and thrower, born August 31st, 1987. He's not especially toolsy and is limited defensively to left field, but there's average power in his bat and he has a good hitting approach, showing little vulnerability to off-speed stuff in Triple-A and catching up with fastballs often enough to produce. His best tool may very well be makeup: no one works harder.
At age 29, Cardullo is not the traditional prospect but you absolutely have to root for him. He's earned this.