CORSAIR JUST ANNOUNCED that every PSU it makes across all three lines has achieved 80 PLUS green certification. As far as we are aware, it's the first maker to hit this mark.
The certification stipulates that the PSUs are at least 80 per cent efficient at 20, 50 and 100 per cent of their rated load - not an easy thing to do at lower loadings.
All HX, TX and VX series PSUs now have this green stamp, so buy three and save a polar bear. ยต
If only they were cheaper... But anyway, 80PLUS is the way to go.
helpful list of available 80plus PSU models & manufacturer links:

http://80plus.org/manu/psu_80plus/psu_join.php

& very handy wattage calculator,

http://www.extreme.outervision.com/powercalc.jsp