If you are looking for an indepth space conquer and colonization game, try: http://ogame.org/
Its free to play and after a few turns you will be sucked into the strategy and addicting playstyle. It is perfect for work, school, or even on portable devices. It plays on any browser and has relatively easy rules.
If you do play, start in universe 43. I am located in galaxy 1, solar system 319 and would love to be allies with all my friends.