One episode of Angel (the one with the children's show puppets) had a kid named "Ratio Hornblower".
Monday Mornings had a nice Actor Allusion. Ioan Gruffudd played a doctor and his boss asked him several times if he was familiar with the concept of "captain of his ship".
In one Honor Harrington novel, the title character is reading a Hornblower book. And, in fact, the whole series had its genesis as a "Hornblower In Space" book; the matching initials are a deliberate Shout-Out and the first book is dedicated to C.S. Forester himself.
In Age of Pirates II, a character named Horatio Hornblower will aid the player if they ask him the right questions.
It's a running joke on this very wiki to call Honor Harrington novels Horatio Hornblower IN SPACE!