I will also give a plug for
www.mtbproject.com as well. I found it super useful on a couple of recent trips. The downloadable maps and the elevation graphs are really nice. Lots of really nice information available there. And the "trails near me" feature is amazing when I find myself done with meetings, in the middle of Michigan, and I have three hours before it is dark. A wonderful tool to make the rest of the day nothing but fun!
I have also used Singletracks for years. And I continue to use it some. Mainly just to locate trails. Not nearly the information about the trails. But a good number of reviews. And just about every trail seems to be on there.
That being said these apps are only as useful as the information sent to them. I just learned that you can have multiple trails on the mtbproject for each trail. I just checked out Quarry Ridge, real nice job Jeff! Now I need to get out and get some different CamRock trails uploaded to there.