Per the Los Angeles Times.

There's no statement from either Brand's camp or the Clipper front office.  Unlike Maggette, who doesn't have any natural suitors, Brand would seem likely to have a couple of serious bidders for his services on the block.  Philadelphia is mentioned as a possible destination, and the Sixers are one of a couple of teams with serious money to spend.

The opt outs clear $24.8M from the Clippers overall number next season, leaving them well under the cap.  The Clippers instantly become The Team With The Most Money to Spend.  They could shower it on Elton or someone else

UPDATE: J.A. Adande has a semi-encouraging quote from Elton in his story on the opt out:

"We're opting out," Brand said. "It definitely doesn't mean I'm leaving the Clippers. We're trying to work it out. My intention is to stay."

...Brand's agent, David Falk, said the forward wants to see the Clippers sign a quality free agent and try to assemble a winning team in Los Angeles.

"It preserves options to make the team better," Falk said. "Clearly, if Elton decided he wanted to simply max out the dollars, he would have stayed in the deal, had a monster year and a lot more teams will have cap room next year."

Interesting.  Falk is basically telling the Clippers that if they want to hang on to Elton, they're going to have go out and spend some money.  It's a kindler, gentler Kobe Bryant game of chicken.

What inspired Brand's decision?  The vibe in Boston:

Falk said a visit to Boston for Game 2 of the NBA Finals influenced Brand's decision to opt out.

"He watched what happened when a few stars get together and agree to have a communal effort," Falk said. "He said 'That's what I'd like to accomplish in my career.'"

What would satisfy Brand?  You have to assume that the Clips would need to do a little better than Beno Udrih.