The original concept behind Castlevania: Lords of Shadow was to remake the original Castlevania starring Simon Belmont. While this idea was ultimately not followed through, Lords of Shadows' protagonist, Gabriel Belmont, wears armor which is reminiscent of Simon's artwork and sprite from Simon's Quest. Lords of Shadow developer David Cox mentioned in an interview that Gabriel is wearing armor similar to Simon's. This is presumably a reference to Gabriel being the first main character of a new Castlevania series, as Simon was of the original franchise.
Gabriel Belmont's basic standing stance and costume are similar to Simon Belmont and Trevor Belmont in the early Castlevania games and box art.
The name of one of the vampire commanders is Olrox. This is the name of a boss in Symphony of the Night, whose character is based on Count Orlok.
A fallen knight mentions a legend that the Bernhard family made a pact with a demon to construct their castle, and because of it's chaotic nature, it's constantly changing. This is similar to what Alucard said about Dracula's Castle to Maria.
It is rumored that Gabriel Belmont is the son of one of the nobles of the Cronqvist family. This is a nod to a character, Mathias Cronqvist, who went on to become Dracula, hinting at Gabriel's ultimate fate.
Another knight in another level mentions starving, and hoping to find food. At the end of his note he says "The 'Cake' is not a lie". This is a nod to the game Portal. In which it is learned that "...the cake is a lie".
In one of the final stages, a Knight Scroll says that Necromancers use Aperture Magic to create their portal mirrors, a reference to Aperture Science, the foundation that cre from Portal.
Day of the Tentacle
In the Abbey Tower level there's a note from a fallen knight who laments upon the deaths of his friends Brother Bernard and Sister Laverne. Bernard and Laverne are two of the three protagonists of classic LucasArts game Day of the Tentacle. Also, the note is signed by "H.", a hint to the third main character from said game, called Hoagie.