So, you just finished a book in a series and you desperately want to read the next one, but you don't know what it's called. You could look at the author's website and hope that it has a list of everything in the series in order. You could do a search in your favorite search engine and hope you don't have to do too much hunting (and hope that none of the sites you click on do something nasty to your computer). But why do all that when you can just use KDL What's Next?
Since I read a lot of series fiction, I use this site a lot. You can search by the author's name, series title, or book title (for instance, the book you just finished). You can also choose to narrow your search down by genre, or by whether or not the intended audience is adults or kids and young teens. Usually I just do a simple author or title search.
And, since I never want to miss an opportunity to say how awesome libraries are (I may be biased, but that doesn't mean it's not true), I'll add that this site is maintained by the Kent District Library in Kent County, Michigan. Nice work, KDL!