Alex, perhaps the best-known parrot in recent history, has died at the age of 31. The cause of death is still being determined (suspected to be aspergillosis, a fungal infection), and is expected to be announced sometime today at a press conference.
Alex was the subject of ongoing research by Dr. Irene Pepperberg. The name is "Alex" is actually an acronym for "Avian Learning EXperiment," and he was noted for his apparent ability to communicate using spoken English, responding to questions and displaying an awareness of quantities (including zero), colors, and a variety of specific objects. Here's more on his abilities from Wikipedia:
Alex had a vocabulary of around 100 words as of 2000, but was exceptional in that he appeared to have understanding of what he said. For example, when Alex was shown an object and is asked about its shape, color, or material, he could label it correctly. If asked the difference between two objects, he also answered that, but if there is no difference between the objects, he said "none." When he was tired of being tested, he will say "I'm gonna go away," and if the researcher displays annoyance, Alex tried to defuse it with the phrase, "I'm sorry." If he said "Wanna banana", but was offered a nut instead, he stared in silence, asked for the banana again, or took the nut and threw it at the researcher. When asked how many objects of a particular color or a particular material are on a tray, he gave the correct answer approximately 80% of the time.
But this doesn't necessarily mean that Alex is "speaking English" in the same way a human would. More from Wikipedia: "However, according to Dr. Pepperberg herself, Alex was not using human language, but rather used 'complex two-way communication.' This means that Alex was able to translate a concept as he understood it into a form comprehensible to humans by using his knowledge of English." Linguist Noam Chomsky argued that Alex's apparent communication skills were merely the result of operant conditioning.
For more general information on Alex, start with this 1999 New York Times article about him, or watch video of Alex from Scientific American Frontiers -- scroll down to the "Entertaining Parrots" segment unless you want to watch the whole episode.
UPDATE: A press release has been posted by The Alex Foundation -- no cause of death determined by the necropsy. The New York Times has a great story summarizing Alex's life and Pepperberg's work with him.