Here are the ATI recommended power supply requirements for the ATI Radeon HD 4890 video card:
500 Watt or greater power supply with two, 75 watt, 6-pin PCI Express® power connectors
600 Watt or greater power supply with four, 75 watt, 6-pin PCI Express® power connectors for ATI CrossFireX™ technology in dual mode.
The recommendations are for an entire pc system.
Corsair and Seasonic are two of the brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. Lately we've been seeing a few other brands offering some high quality units.
AMW1011 - That's easy. The best model series PC Power & Cooling ever had was the Silencer series. Those psu's were manufactured by Seasonic for PCP&C. The Silencer series is getting hard to come by in the USA. Newegg has only one model. Amazon has only two models. Similar situation at other vendors in the USA. Not much better for the Turbo Cool series either. If you go to the PCP&C cooling web site they list 33 psu's. Only 3 or 4 appear to be available in the USA. If you look at their list of reviews you will notice that they are almost all European reviews and only for a couple of psu's. There are a few Asian reviews and one Australian review on the second page of the awards list. JonnyGuru hasn't done a PCP&C review since 2007. Tom's Hardware 2009 Gift Guide made the list but it was for an uninterruptible power supply. It hasn't been the same since OCZ acquired PCP&C.
I used to include PCP&C in my recommendations but there's no point in saying a psu is awesome if it is not available.