http://www.johnnylucky.org/power-supplies/psu-recommendations.html here are some generally recommended power supplies. for the price, the xfx, seasonic and evga "2" series are usually the best buys. the other quality psu's are usually a lot more expensive. the xfx 550w, seasonic 620w and evga b2 and g2 psu's are usually well priced around $50.
what you are looking for is both quality internal parts, the list above uses good parts, and high efficiency. many cheap psu's won't provide anywhere near the power they say they will. the quality brands will put out what they say they will.
the 270x will perform better than the 270. as far as cooling goes, each brand has it's high points and low points. better cooling usually means more noise from the fans but most of the cards use their own cooling and work well and pretty quietly. i have both the 270 and 270x in my house and they run cool and quiet for me. (all are HIS brand cards but i will not recommend them due to some shady business practices they chose to use)
as for the ram, crucial ballistix is plenty good enough and good ram.