To Nnk:
I've had problems initializing a card also, it turned out I had a bad contact between my card reader board and the header it was sitting upon. I soldered everything and it works perfectly now. You might want to verify all the electrical contacts, just to be sure.
Good luck!
Note: I use the very same circuit that you are using, except for 2 additional 100nF and 47uF capacitors between the 3.3V and GND pins next to the card (it probably works without that). I use a 2GB SD San Disk card.