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 episode of Star Trek: Deep Space Nine, Jake Sisko is editing a manuscript, but sharp-eyed viewers can spot that the text is from Commodore Hornblower. Appropriate, as Star Trek took in a lot of inspiration from Hornblower.
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.