11:40 EST: Of all the condolences and memorials people are offering, perhaps the one from Shirley Sherrod has been the most hotly anticipated. The former USDA official was forced to resign after Breitbart posted part of a video of a speech that made her appear racist, but turned out to be only a part of a longer tale of racial healing. The White House later apologized to Sherrod for asking her to leave. On Thursday, Sherrod released this brief statement, which Talking Points Memo posted:

"The news of Mr. Breitbart's death came as a surprise to me when I was informed of it this morning. My prayers go out to Mr. Breitbart's family as they cope through this very difficult time."

11:27 a.m. EST: Newt Gingrich has also weighed in, first tweeting: "Andrew Breitbart's sudden death is a tragedy for his family and for conservatism. Callista and I send our prayers and our condolences." And following up with: "Andrew Breitbart was the most innovative pioneer in conservative activist social media in America. He had great courage and creativity."

11:19 a.m. EST: Breitbart's former colleagues have been offering some more substantial memorials to him. Arianna Huffington, who Breitbart helped launch the Huffington Post, wrote in an email to Forbes' Jeff Bercovici: "All I can think of at the moment is what Andrew meant to me as a friend, starting from when we worked together — his passion, his exuberance, his fearlessness. And above all, what I’m thinking of at the moment is his amazing wife Susie and their four beautiful young children. My love and thoughts are with them right now."

Matt Drudge, for whom Breitbart previously worked as a reporter, posted his thoughts on Drudge Report:

DEAR READER: In the first decade of the DRUDGEREPORT Andrew Breitbart was a constant source of energy, passion and commitment. We shared a love of headlines, a love of the news, an excitement about what's happening. I don't think there was a single day during that time when we did not flash each other or laugh with each other, or challenge each other. I still see him in my mind's eye in Venice Beach, the sunny day I met him. He was in his mid 20's. It was all there. He had a wonderful, loving family and we all feel great sadness for them today... MDRUDGE

10:52 a.m. EST: Mitt Romney tweeted his reaction to Breitbart's death: "Ann and I are deeply saddened by the passing of @AndrewBreitbart: brilliant entrepreneur, fearless conservative, loving husband and father."

10:42 a.m. EST: Media Matters, the liberal watchdog with which Breitbart often sparred, has disabled comments on its brief post on Breitbart's death, Talking Points Memo reporter Evan McMorris-Santoro pointed out. The site's final word on Breitbart: "We've disagreed more than we've found common ground, but there was never any question of Andrew's passion for and commitment to what he believed."

10:26 a.m. EST: We still haven't learned a cause of death, but the Associated Press is reporting Breitbart collapsed while out walking shortly before his death:

Breitbart was walking near his house in the Brentwood neighborhood shortly after midnight Thursday when he collapsed, his father-in-law Orson Bean said.

Someone saw him fall and called paramedics, who tried to revive him. They rushed him to the emergency room at Ronald Reagan UCLA Medical Center in Los Angeles, Bean said.

Breitbart had suffered heart problems a year earlier, but Bean said he could not pinpoint what happened.

10:04 a.m. EST: Politico's Juana Summers tweeted this quote from Rick Santorum: "What a huge loss, in my opinion for our country and certainly for the conservative movement. My prayers go out to his family." House Majority Leader Eric Cantor had this to say: "I'm stunned to hear about the passing of Andrew Breitbart. My thoughts and prayers are with his wife Susie, his children, and his friends."

9:38 a.m. EST: The tributes to Breitbart are already flooding Twitter as fans and colleagues remember the breakout right-wing media star. Reuters' Felix Salmon tweeted "I didn't like his politics, but the man grokked the internet like few others," referring to Breitbart's near-uncanny ability to land his points with readers online. Wired recognized that ability in its lengthy 2010 profile on Breitbart, which elaborated on his skill at "hacking the media." Milwaukee talk show host Vicki McKenna was among the many on Twitter lauding Breitbart as a hero to his movement. "we have lost a hero today. the amazing andrew breitbart has passed away," she tweeted. Even notable left-wing activist Russel Simmons lauded Breitbart as he offered condolences to the family: "Political differences aside, he was a great patriot."

9:30 a.m. EST: Good Morning America producer Katie Bosland tweets that Breitbart's death has been confirmed: "LA Coroner’s Office has confirmed to @ABC that Andrew Breitbart passed away last night at UCLA Medical Center."

Original: Andrew Breitbart's news sites Big Journalism and Big Government, are reporting the death of their founder shortly after midnight in Los Angeles. "Andrew passed away unexpectedly from natural causes shortly after midnight this morning in Los Angeles," his sites report. Breitbart was 43. Asked to confirm the news, Joel Pollak, editor-in-chief of Breitbart.com, told The Atlantic Wire by email, "I can't tell you more than I have already, unfortunately. We'll know more later." Ben Howe, a Breitbart colleague, tweets that he has "personal confirmation" the news is legitimate and not a hoax as some on Twitter had initially suspected. "We have lost a husband, a father, a son, a brother, a dear friend, a patriot and a happy warrior," wrote Larry Solov in the announcement on Breitbart's sites.