Here is a website I use for helping people I know choose the right PSU for their system. It may be complicated but it gives a good conservative comprehensive estimate.http://extreme.outervision.com/psucalculatorlite.jsp
Minimum PSU Wattage: 418 Watts
Recommended Wattage: 468 Watts
Thats with everything on your post factored in with aging over a 2 or 3 year period. Sorry I'm a overkill pro. So a 550W would be just fine as stated earlier unless in the future you wanted to get another 680(In which case a 650W would be not enough).
NOTE: ONLY FOR INFORMATION. There are more complicated things dealing with the rails and their output amperage, but that really only applies to overclocking, multi-video card setups, and having loads of peripheral devices(aka you should be fine). Also if you plan on building many systems in the future buying a PSU tester is not a bad idea because a bad PSU can make you cry when you start the system.