Here are some links to popular websites with theatre connections. Any links which require subscriptions have been omitted. LINK– The most comprehensive website devoted to Theatre in the UK: listings, reviews, news, gossip,  discussion, features, prizes, special offers, etc. 
Playbill LINK Everything you ever wanted to know (and more) about what’s happening on Broadway. Daily updates of news, gossip, reviews and lots, lots more
theatreCat LINK Libby Purves, ex-chief theatre critic of the Times newspaper, now independent, remains one of the best theatre critics around although her reviews are limited in number.
Guardian Newspaper LINK Theatre reviews from the newspaper of choice for the still chattering classes LINK This is the BEST website for on-line reviews