As the title says, what is your favorite alien race in Sci-Fi? It could be anything that derives from TV, movies, games, books, whatever you want. Maybe even post a picture to show off or post some backstory to explain why.
My personal favorite would be the Necron's from Warhammer 40k followed closely by the Protoss in StarCraft.
For those that might not know, the Necron's are a race that originally formed from a species called the Necrontyr which were deceived by promises of immortality, 60 million years prior to the events of W40k . They were promised immortality but they paid the price to be forever imprisoned in soulless metal skeletons and husks built for war and conquest.
After exacting revenge on their deceivers, they slept until the events of W40k where they awoken to reclaim the galaxy.
Necron's are regarded by many as having technology so advanced that their basic weapons cripple the most advanced weapons of many other species and dumbfound their top researchers and scientists. I'd probably go as far to they are the most advanced alien race in all Sci-Fi.