There's an essay about this cat in the latest New England Journal of Medicine. I can't forward that around (as much as I would like to), but here's the link to the CNN story. This cat lives in a nursing home and predicts when people are going to die - he simply goes to their room and curls up next to them. According to the article, "His mere presence at the bedside is viewed by physicians and nursing home staff as an almost absolute indicator of impending death, allowing staff members to adequately notify families. Oscar has also provided companionship to those who would otherwise have died alone."
If you have access to the NEJM, I'd recommend reading the original essay by Dr. Dosa. It's in the July 26, 2007 issue ( vol.357, p.328-9). If not, searching "Oscar the cat" on Google News brings up quite a few hits.