Imre Lakatos was one of the most influential writers in twentieth century philosophy of science. Though the title is usually reserved for Karl Popper or Thomas Kuhn, it is actually Lakatos' contributions which have survived through most of the critics.
Lakatos argues that science should be not be evaluated according to the blind falsifiability criterion of Popper; nor should it be rejected as essentially a social excercise with little relation to objective reality, as Kuhn would argue. Instead, he argued that science should be understood as the development of research programs - some of which are progressive, and generate genuinely new theoretical and empirical results, others of which are degenerate and find themselves constantly drawn back to certain fundamental theoretical difficulties, and seem not to generate any new, positive results.
Lakatos also argued that the problem with Popper's falsificationism was that it was naive. He claimed that Popper was essentially right, that science rejects theories when they fail to accord with observed fact, but added the essential observation that this only occurs when there is a competing theory which explains the fact. In short then, Popper argued that science recognised failures, and then generated new theories, which is intuitive but bogus. Lakatos says that we can recognise failures and keep a theory, if it's useful, but we will reject it when a better theory comes along. He's a smart guy like that.
A fun and, I'm told, true story about Lakatos involves the fact that he was Polish and living a little too close to the Germans in WWII. Unlike a lot of academics at the time, he did not flee to the U.S. and was captured by the German SS. He was interrogated by an SS officer for a solid week, during which time he was so infuriating in his answers, and so resistant to the pressuring of his interrogator that after a week had passed, the SS officer in charge of his interrogation walked into Lakatos' room and shot himself in the head. How cool is that?