There are many other species similar to Aliens and Predator, and here are a few:

THE ZERG
The Zerg are an alien race from the computer game 'StarCraft'.

THE PROTOSS
The protoss don't really look like predator, but their nature a the way they act is very similar. They are also from StarCraft.
NOTE: StarCraft is an incredible game and you should get it.

THE TYRANIDS
Tyranids are one hell of an alien race who are from Games Workshop's tabletop wargame, WarHammer 40,000 (Or just 40k). They are even more similar to zerg than aliens, and I collect a Tyranid army if anyone actually cares.

THE SKAARJ
Skaarj are the race of very savage aliens from the computer game 'Unreal'. They look like predator, act and sometimes sound like predator.

If you find any more races that are like Aliens or Predator E-mail me with a picture of the species and I'll actually put them up here.