@Shadi:
Just because a card is double slot, doesn't mean it has high power consumption, it only means that it has better cooling.
Anyway, about good mid-end graphics cards with relatively low power consumption, you can't go wrong with the Radeon HD5750, Radeon HD5770, or Radeon HD6850. These 3 only require one 6-pin pci-express power connector, with the HD5750 having a TDP of 86W, HD5770 having a TDP of 108W, and the HD6850 having a TDP of 127W.