I'd recommend Colony.
After an alien takeover, LA becomes an isolated colony ruled by the invaders through their human agents.
The basic set-up is strong. We never see the aliens - their physical presence is represented by sinister flying drones - so the tension lies between the 'collaborators' who rule in the aliens' name, the ordinary population who mostly try to keep their heads down and survive, and a small resistance movement who kill collaborators and plant bombs.
This conflict is effectively dramatized in a single family where the father, an ex-soldier, works for the authorities, and the mother, unknown to him, is a resistance fighter.
The show does a good job of retaining moral ambiguity - there are decent people on both sides - and with all kinds of mixed motives in play and the aliens ultimate plans unrevealed, it's not clear which is truly the 'right' side.
It's not as heavy and self-serious as something like Battlestar Galactica, and never forgets its job is to entertain, but still asks a lot of interesting questions about its characters behaviour in life or death dilemmas.
Josh Holloway, the guy from Lost, makes an appealing hero, and Sarah Wayne Callies, playing his wife, is an attractive mixture of strong-mindedness, vulnerability and femininity.
Best of all it's got loads of petrol in the tank. After 7 episodes, we have yet to see an alien or learn anything about them; we don't know who they are, why they came, what they're doing now or intend to do in the future. So the show is in no danger of running out of steam.