As a counter-point to my somewhat flippant previous answer (which only really applies if one is a specialist in the field), if you are looking at a field in which you are not as much a specialist in, I suggest reading the articles from the Bulletin of the AMS. The articles are designed to be fairly up-to-date and expository in nature, and often gives the state of the art in their reviews.
Of course, a similar caveat as that to Helge's answer applies: the "news" maybe several months out of date. But considering the glacial paces at which a lot of mathematical refereeing takes place, I think it is quite okay.
In the spirit of this answer, you may also find http://mathoverflow.net/questions/15366/which-journals-publish-expository-work to be useful.