A writing acquaintance -- in fact, a woman with dozens of books to her credit, sent me this link a few days ago, saying "I have a friend pretty impressed with an agent she found there, but there are lots of others."
The site is "Agent Query, the Internet's largest and most current database of literary agents."
It's apparently a free service. Here are some relevant quotes from the site's "About" page.
"Agent Query offers the internet’s only searchable database of over 900 reputable literary agents—for 100% free. That’s right—free. No login or monthly subscription fees to browse our database ...
" ... our AQ database was created from sheer, mind-numbing research, countless irreplaceable hours of tedious data entry, grinding computer programming, and psycho-obsessive determination. We created it. We maintain it. And we decide—like a bouncer at a trendy club—who’s in and who’s not ...
" ... free is fun ... we’re not internet entrepreneurs. We just want to help writers. The main reason we created Agent Query was because we were sick to death of spending hour after hour, trolling through random website after random website, just to glean teeny weeny bits of information about a handful of literary agents ... thank us later in the acknowledgements of your first published book."
The logical and expected disclaimer: The Internet Writing Workshop and its administrators individually or collectively cannot vouch for any claims or promises made by other people or organizations. Writing, as with other things in life like buying a used car, is always caveat emptor.