The only online "tools" I use are blogs and review sites whose tastes I've become familiar with. And "What are you reading now" threads on forums I frequent enough to know who likes (and who dislikes) what. "Word of mouth" still works on the internet.
That and I don't worry too much about picking up an author that I may not
like. I just stop reading that (if I find it unbearable) and turn to something else.
Reading by the boatload's still the best "tool" though. There's really no shortcuts to finding new authors you love. I, for one, hope there never is. Part of the journey, and all.