My existing supply is an Antec SP-450. This is a 450 watt supply that I would have thought was a decent supply back around 2008 or so. It is now about 5 years old, and doing some research on it, I find that it was not well thought of even in its day. It gets a "two egg" rating on the NewEgg site, with 48 percent of the ratings giving it one star. Lots of people had this supply die with capacitor problems. Some people lost hard drives and motherboards when the supply went. A lot of this was due to bad capacitors, and this was acknowledged by Antec. I guess mine was from after they got the capacitor issue sorted out given that it is still humming along nicely in 2013. Yields 3.3/32, 5/30 12/15+17 - I am not clear on the split rating on the 12 volt supply.
Given the age and reputation of this supply, I think it would be wise to replace it. Also it only has a 4 pin auxiliary power connector, and my new LGA1155 motherboard has an 8 pin auxiliary connector.
Note that the 4 or 8 pin auxiliary power connector carries 12 volts and ground -- and the 8 pin version simply adds two additional 12 volt and ground connections for extra current.
Seasonic supplies get spectacular reviews. Corsair seems pretty good, as well as Cooler Master. I am looking at the Corsair CX-600. It yields 3.3/25, 5/25, 12/46 -- note the extra +12 amperage. This is apparently what is delivered via the 8 pin auxiliary connector.