Nathan Phillips- Maybe it's just not his time, but I remember hearing a few people speculate that he was likely to go somewhere. After he did Snakes on a Plane and Redline, I haven't seen him. It seems he's become more B-level, especially with one of his movies being released on Horrorfest 3.
Steve Guttenberg- He still acts, but when's the last time we've actually seen him in a theatrical film? It Takes Two? Even though he did a good number of 80's comedies outside Police Academy, he'll forever be known as Mahoney.
I did see him yesterday on an infomercial for the Total Gym but I am not sure how old the ad was.