I wouldn't recommend buying any of the 'mainstream' to 'high-end' (600W or more) PSUs listed in this thread. They're pretty expensive ($70+) and are over what you need, especially since it seems like you're on a budget.
Here's what I'd use to determine how much wattage you need
PSU Calc then select a sufficient PSU from the
recommended PSU list.
Without any overclocking (2 RAM, 1 HDD, 1 SSD, 1 Optical, 4 Fans) you're going to be looking at 325W for an A8 + 7870. (375W for 7950). Overclocking would bump you up about 100W.
Assuming your total budget for these two parts is $350, I'd go with one of the following:
CX 430 v2 $25 after $20 MIR +
AMD 7850 $170 to $190 or
AMD 7870 $210 to $250 or
Nvidia 660 $180-$220
XFX Core 550W $60 +
AMD 7950 $270 to $330 or
Nvidia 660 Ti $270 to $300.
Here's the performance hierarchy for the above recommended cards -
AMD 7850 < AMD 7870 = Nvidia 660 < AMD 7950 = Nvidia 660 Ti
Here's the manufacturer hierarchy -
ASUS = MSI = Gigabyte = EVGA > Sapphire = XFX = Zotac > HIS. I'd shoot for Sapphire/XFX/Zotac. I have restricted the PCPartpicker lists to these manufacturers.
For the 7850, I'd shoot for the 2GB version if its at least $30 cheaper than 7870 (equivalently ranked manufacturers).