Valve is Open to Acquisition Talks

Doug Lombardi, in an interview with Gamasutra, stated that Valve would "happy to have that conversation" to any parties interested in acquiring Valve.
"By the same token, the company's doing pretty well, and we're really happy with what we're doing," he added.

"So we'll see. I mean, anything is possible."
Lombardi also discusses how Valve was one of the deciding factors in John Carmack's decision to move to EA as a publisher.
In Gamasutra's recent interview with id founder Carmack, he said he had prejudices about EA that he discussed ahead of forming a deal with the company, and one of his sounding boards was Valve.

"Yeah, yeah. Well, [Valve managing director] Gabe [Newell] had the same reaction when [COO] Scott [Lynch] and I came home from our roadshow of meeting with all the publishers, and we said, 'We think EA's the right choice.' He's like, 'You've got to be kidding me!'"

But once Newell met with those whom Lombardi called "the people that had impressed us," he relented.

"And we set up the deal so that it turned out that if EA was this evil empire, that it wasn't going to last forever," Lombardi said. "But it's turned out that all those scary stories - which, you know, maybe some of them were true, and maybe some of them are history; I don't know - haven't appeared to us; we haven't seen the boogeyman."
Valve really seems to enjoy their working relationship with EA. For more, head on over to Gamasutra.