Include case fans, optical drives, connected USB / firewire, anything esle on the list
Use 85% TDP, 90 % CPU load and 25% capacitor aging.
After ya done, multiply by a headroom factor between 1.1 and 1.5 ..... go towards higher end of that range the more ya want .... multiple cards, OC'ing, how stable you want your voltages, how efficient you want PSU to run, how long you want everything to last.
Any decent 400w power supply (Corsair, OCZ, Seasonic, etc.) would have no problem powering your system with the 4670. You'd only need more power if you intend to upgrade your graphic card to a more powerful unit in the future.
The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the 12 volt rail(s) can easily power a system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the 12 volt rail(s) can power a system with two video cards operating in dual mode. There are a few exceptions like the new ATI Radeon HD 5XXX series cards which use less power due to their energy efficiency.
Before purchasing a new psu you will need to decide whether you will eventually have a pc with one or two video cards.
Corsair, PC Power & Cooling, and Seasonic are some 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. Lately we've been seeing a few other brands offering some high quality units.
The difference between modular and non-modular power supplies is insignificant for the typical user. Instead, it is a matter of personal preference.
If you do not plan on using two video cards, then the Corsair VX550 is a very good buy right now at newegg.com. Between the sale price, free shipping, and a mail-in rebate, the final price is $59.99: