The Skaarj are heavily inspired by Predator, including such homages as dreadlocks and wrist-mounted blades.
The second single-player level, "Nyleve's Falls" is named after the levelmaker's*
Juan Pancho "Xceptone" Eekels
wife.
The Vortex Rikers registration number (NC114-85EKLS) is a reference to him, as well.
All the names in the translator logs belong to many of his friends.
The ninth level, also made by Eekels, is called Harobed Village.
In the level "Bluff Eversmoking", there's a tombstone marked "Myscha"*
which is the name of its levelmaker, Elliott "Myscha" Cannon
In the first mission of Return To Na Pali, "Edge Of Na Pali", near the end, after you killed the Pack Hunters and opened a locked the door, when you go outside, near the crashed ship, you can find a dead soldier under the name M. Worch. Matthias Worch is one of the Legend Entertainment developers.
There's another one, at the beginning. When you exit from the building you start, you'll find a guy drown at the lake. His name is W. Marshall. Warren Marshall is one of Epic Games's employees.
The map "Glathriel Village", also from Return To Na Pali, has an Easter Egg which guides to a secret. It has the Unreal Tournamentclan Ocrana's logo, and the translator has the following message:
DM-Morpheus is inspired by a scene from The Matrix, and its name was taken from Morpheus, one of the main characters.
AS-Overlord ("Operation Overlord") is inspired by D-Day.
When you play in the campaign, in the Venom team, two of the characters are named Ada and Lovelace, a Shout Out to the (arguably) first programmer in the world.