The award-winning Portal, part of the Orange Box collection released last fall, was apparently a candidate for XBLA at one point. Following it’s rejection, Valve’s marketing director, Doug Lombardi explains, 

"We’d love to do that. Right now it’s something we’d love to do. I’d love to sell Portal on Xbox Live,"

Despite his enthusiasm, Portal was likely rejected due to size restrictions and other complications. The thing is, Microsoft recently increased the file size for titles on XBLA - from 50MB to 150MB.

Lombardi, however, remains hopeful for Portal, "…it’s been proven now on Steam, so I’m sure it’ll migrate back to the consoles just like everything else does"

Thanks to GamesIndustry.biz