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:
http://www.newegg.com/Product/Prod [...] 6817139004
It is a bit more power than you need for a system with a 4670 video card but you would be prepared for any single videoo card upgrade for the next 5 years.