Here are some alien species who supported the Empire:

1. The Noghri 
http://starwars.wikia.com/wiki/Noghri

2. The Ailon
http://starwars.wikia.com/wiki/Ailon_(species)
3. The Chevins
http://starwars.wikia.com/wiki/Chevin/Legends
4. Devarians
http://starwars.wikia.com/wiki/Devaronian/Legends
5. Many Rodians served the Empire as Bounty Hunters, Rodians are known as good bounty hunters. Most did it for the money, rather than loyalty for the Empire. http://starwars.wikia.com/wiki/Rodian/Legends

6. The Muuns
http://starwars.wikia.com/wiki/Muun/Legends
7. The Umbarans http://starwars.wikia.com/wiki/Umbaran/Legends

8. The Trandoshans 
http://starwars.wikia.com/wiki/Trandoshan/Legends
9. Flakax
http://starwars.wikia.com/wiki/Flakax
10. The Company SoroSuub which was run by Sullustans was a early supporter of the Empire, although a fair number of Sullustans joined the rebellion http://starwars.wikia.com/wiki/Sullustan/Legends

(By the way, this is a great discussion about species loyal to the Empire. It has some species that I haven't mentioned)
http://boards.theforce.net/threads/alien-races-allied-with-the-empire.50003617/