First up is What Should I Read Next?
What I like about this site is that it has a direct link to Amazon if you'd like to buy it and every title has several keywords under them, telling you what the book is about.
You can also create an account and start creating lists for books you've read or wanna read, but I find this feature to be too simple and for that I like using Goodreads better.
What's useful about this website is that you can search other people's lists (listopia), so if you need books about the 1st day of school or books about art you can find lists on the subject. Even Goodreads make their own lists. Now be prepare to spent several minutes going through their search since it is not the best one and sometimes the names of the lists aren't very useful, but if you know of a book and you want similar books to it I suggest searching for the one you know and starting there.
I know there's a lot more websites out there (Pulse it, Riffle, Shelf Awareness) and even Pinterest is a great resource (Lawrence Public Library) or Instagram (NYPL), but this are the ones I use the most. Hope you find them as useful as me and if you have any suggestions let me know in the comments below!