They are efficiency certifications awarded by the 80 Plus organisation. PSU manufacturers have to submit models for testing in order to use the 80 Plus logo. Just a word of warning though, there have been cheap manufacturers fraudulently using 80 Plus logo's on their PSU's (none of the ones you mention above, I'm just making the comment for general info). Certified models are listed on the 80 Plus site. The different levels of rating are described on the 80 Plus website or here. The highest is Titanium, although I'm not aware of models released with that certification yet. Platinum then is the best efficiency rated PSU's you can easily buy at the moment.
A more efficient PSU means lower energy use, as less power is wasted as excess heat. A PSU operating at say, 70% efficiency delivering 400w will actually be drawing 571 watts from the wall socket. The 171w is wasted energy. While a PSU operating at 90% efficiency delivering 400w will be drawing 444w. That's a fairly big difference.
It's also in some ways a proxy for the quality of the power supply - low quality cheap PSU's tend to be very inefficient. In order to be certified they have to be tested as at least being able to deliver their rated power at the required efficiency level. In order to be Gold certified, for example, they have to be able to deliver 100% load at 87% efficiency. A low quality PSU simply cannot do this. Low quality PSU's tend to struggle to achieve their rated output, if they can even reach it at all. However if selecting parts for myself I wouldn't just go on 80 Plus rating alone, and would search out a review on one of the numerous enthusiast sites who test PSU's in incredible detail.
One criticism of the certification is that it's done at relatively low temperatures of 23 degrees as mentioned here. In reality, the inside of a PC case is likely to be much warmer than that. And higher temperatures generally equal lower efficiencies.