The Power Supply Requirement for your system is:
450 Watt or greater power supply with 75 Watt 6-pin PCI Express® power connector recommended (550 Watt and two 6-pin connectors for ATI CrossFireX technology in dual mode).
As other people has said before, the CORSAIR CX400 is a very good PSU which can handle your system. Anyway, for a few more bucks you can get a CORSAIR VX450 or an ANTEC EarthWatts 500W, which are better choices.
Anyhow, if you decide to save some bucks and go for the CX, you won't be disappointed.