Something or another recently reminded me of Mystery Team, which starred Donald Glover and Aubrey Plaza before Community and Parks and Recreations. Any other favorite independent/tiny release films starring people who later made it big?
Mad Max!
Safety Not Guaranteed
Jennifer Lawrence in Winter’s Bone.
People may forget that even though the film was nominated in four Oscar categories, including a Best Actress nod for Ms. Lawrence, Jennifer Lawrence’s claim to fame when this film opened was playing the mouthy daughter on The Bill Engvall Show.
And, because Debra Granik is so good at creating famous actresses, I’m going to be the first to call out Thomasin McKenzie in Leave No Trace. Remember, you read it here first. 
Not sure if I would call it a “favorite”, but I was watching “Garden State” and recognized a then-lesser-known Jim Parsons…as an odd character (but not quite Sheldon-like).
Never realized that Winter’s Bone played on so few screens. I seem to recall it getting lots of press when it was out.
The Wanderers. The Wanderers (1979) - IMDb
Ken Wahl and Karen Allen were the big names. The large cast contained many familiar faces.
River’s Edge with Keanu Reeves.
Blood Simple starred Frances McDormand.
Gallipoli
The Return of the Secaucus Seven had among it’s ensemble cast, future Emmy-winner Gordon Clapp, who would play the well-meaning, likable, not-the-brightest-bulb Det. Medavoy on NYPD Blue, and would forever play nice guys who were not so bright, except when the surprise twist at the end of the story was that his “aw, shucks” demeanor masked a serial killer, or something.
In Secaucus 7, he plays a very sharp, very clever, Senatorial speechwriter and Washington insider, who, in spite of his Boy Scout demeanor, usually has weed. I saw that movies several times, and completely failed to recognize him.
Dazed and Confused - Matthew McConaughey, Ben Affleck
Also David Straithairn, who has a long list of movie and TV credits afterwards.
Another actor from a John Sales movie is Joe Morton from his Brother from Another Planet, who became successful as Rowan Pope in Scandal. His Matawan had Chris Cooper and Mary McDonnell.
Of course the Rocky Horror Picture Show with Tim Curry, Susan Sarandon and Meat Loaf!