A showing of intent for both Portal and Half-Life movies was made years ago by J.J. Abrams and Gabe Newell at DICE. Since then though, the projects have mostly been silent though.
However, they are still on their way to being made apparently. Speaking in his Reddit AMA last night, Newell took this question on directly, and confirmed that both movies are on the way. He said simply:
Yep. They're still coming.
Video game movies are 'in', at the moment, so I wouldn't be entirely surprised if over the last year or so, movement on these has been a little more accelerated. However, we are seemingly still very far from a release date or anything if these movies ever see the day.