Change has been gradual. There are several events that have acted as turning points, however.

The Stonewall Riot is usually the first thing that comes to mind, and is chronologically the first really big turning point (not to discount earlier moments of activism, because they did exist and they were important.) The riots helped to create a certain kind of openness, and resulted in a more public and more assertive gay and lesbian movement. Unfortunately the trans* women of color who were predominate in the riots and the early days of the movement were largely pushed out of the dominant forms of activism.

The 1986 Supreme Court case, Bowers v. Hardwick, was another major turning point. Bowers upheld a Georgia law that criminalized homosexual sex, even between consenting adults in the privacy of their homes. This event galvanized AIDS activists, who were confronted with the harsh realities of a homophobic society and government. After several years centered around lobbying and caretaking efforts, the community began to move towards confrontational activism. It was the work of ACT UP and others that brought about many of the significant changes in regards to AIDS policy and gay and lesbian acceptance more broadly.

The most recent turning points have been largely centered around state and federal policies around same sex marriage, as well as representational advances in regards to film, television, and public figures. That gets more into current events, however. Certainly change has happened both gradually and through more specific events like the two described above.