These specially bred types of Alien are unique to Aliens vs Predator, and will probably make an apearance in the Alien 5 or Alien vs Predator movies.
First a bit of an idea of how life is in the hive, in my opinion.
Hive Ecology - Alien hive life is similar to that of a Termite or Ant hive. There is a central female that controls the rest of the hive. The fact that there is a dominant male is unknown. Drones carry the eggs around to different nesting chambers while others hunt. The "Architect" drones expand the resin of the hive and build new strands to support the decayed ones from the queen's supports. Captured victims hang off the walls floors and even ceilings, many of which have already chestbursted. Praetorians gaurd the queen, runners scout out new locations for the hive to take control of. And now to the strains:
Runner - These are called "dogs" by marines, due to their dog like apearance, Runners are the most unique of the drones. They always are on all fours and are extremely fast. They are also the most frail type of Drone used by the hive, due to their low strength and integrity. Their small size also allows them to fit into secure places. The Alien from Alien 3 was an example of a Runner.
Praetorian - Named after the Imperial Gaurds of Roman Emperors, Praetorians suit their name well. Found in special areas of the hive, mostly around the Queen. They have a heavier Exoskeleton than other drones and are slightly slower then other strains, and can't climb walls. The heavier armor allows them to resist small caliber fire and flame. Praetorians also share some common features with the Queens. They have the same 3-pronged "crown", the six pointed dorsal spikes instead of the Drones' 4 tubular dorsal spikes. Praetorians also have an unusual foot design compared to the other drones, a hoof shaped foot. Praetorians are also immense in size, standing 13-14 ft tall. Praetorians have most things that a normal drone has, double jaw, tail, and decent speed. Due to the Praetorian's increased leg muscles, Praetorians can jump extremely high. Drones can molt into a Praetorian, provided they have access to certain hormones emitted by a queen. If they morph, they must leave the hive until the hormones have deteriorated. The pheromones will drive the hive crazy and will try to kill the Praetorian. The Praetorian can re-enter the hive after several days. Examples of drones beginning to molt into praetorians are the two that were protecting the Queen in Aliens.
Predalien - Next to the Newborn, the Predalien is another genetic mutation. Created by the combining of Predator and Alien DNA, Weyland Yutani created a creature with the strength and durability of a Predator and the speed of an Alien. Predaliens are ugly by most account. They have a tan-colored skin and predator-like facial features, including dreadlocks. The Predalien's mouth configuration disables its ability to head bite. The first specimen of a Predalien was encountered and killed by a Predator on LV-426 (many years after the Hadley's Hope incedent.) The Predalien became known as an official strain, since aliens have began capturing Predators for Chestburster hosts. Due to its heavy armor and predator like distinction, Predaliens are the slowest type of strain ever reported. Predaliens are also extremly territorial and will not hesitate to kill anyone who enters their territory, even a fellow alien.
Empress - The mother of all of the aliens. Not much is known about this massive creature, except it has a 5 pronged crown instead of the normal 3. She is also known as the Queen of Queens.
Sources: My knowledge, Aliens, Alien 3, Aliens vs Predator 1 & 2.