Evaluating Beer isn't too badly dated. It's a mixed bag of articles from various sources, and while some of the information is very good, it just isn't a particularly enjoyable read.
Mosher's Tasting Beer, though, is an instant classic. If you're an experienced brewer and beer geek, then you might not find a whole lot you don't already know. Nonetheless, what John Palmer has done for brewing beer at home, Mosher has done for tasting and appreciating beer.