I have just noticed that Armor Mayhem by @Louissi is just too good to not be on my favourite online games list. Earlier it was just on my good games list. So here it is:

1. Dino Run!

2. Scuba

3. Pingy the Ping Idle RPG

4. Everybody Edits -- played daily since february 2012

5. Flipside

6. Seedling

7. Wooden Path

8. Shields of Gemland

9. Mega Miner

10. Blob Drop!

11. Viking defense

12. Red Ball

13. Hello Worlds!

14. Lint

15. Armor Mayhem

16. PaintBall - The Game

17. Learn To Fly (also LTF2)

18. Tank In Action

19. K.O.L.M

20. Mini Train

Here is my good games list(not in any particular order):

Super D

Riddle School series

Uphill Rush

Umbross

HarryThe Hamster 2

Sand Castle

Bionoids

BR's Climate Chaos

Flingo

Get Off My Lawn

You Are The Road

Axon

Bartender: The Mix

wOne

Deep Diver

Ectology

Moonlight Differences

Scriball

Hexagon

Stick Figure Badminton 2

Mutiny

Acid Bunny

Endeavor

Simgirls

Nekra Psaria series

Most of these games are pretty old and that is because I enjoyed games more as a kid.

There are much more great games out there so keep playing and you may find something you really like!