I'm considering buying a flash for my Canon DSLR. I noticed the 600EX recently came out. Do you have any suggestions/opinions about the pros and cons of the new 600 flash versus the other two?
Price vs Radio wireless, I have a 600EX-RT and I love it. The wireless radio is the big upgrade. It should support far more complex wireless flash operation, though currently it only works with more of the 600EX-RT flash units. (Presumably there will be more devices in the RT line down the road.)
I don't know if the flash bulb moves to adjust the guide number in the 480EX or not, but I believe it does in the 580EX. I know it does in the 600EX-RT which is a pretty nice feature. The menu system on the 600EX-RT is also very nice and will work very easily through the camera's menu system as well on newer cameras.
So main pros for the 600EX-RT that I notice are the newer design (backlit LCD screen with easy to use controls), wireless radio sync (no line of sight limitation/longer range/more control) and cons are higher price.
If you plan on taking advantage of the radio wireless TTL capabilities of the 600EX-RT, either now or in the future, you will either need another 600EX-RT or the ST-E3-RT to use as a transmitter. Some third party wireless triggers, such as those offered by Pocket Wizard, will also allow wireless TTL operation of Canon flashes including all three that you mentioned in your question. Each option adds considerable expense to the price of a single 600EX-RT.
If you plan on using the flash mounted on camera or connected by a hot shoe cable the 580EX-II or the 430EX-II offer more bang for the buck. The biggest difference between the 580EX-II and 430EX-II is the maximum flash power for each unit. The respective guide numbers for the 600EX-RT, 580EX-II, and 430EX-II in feet @ ISO 100 are 197, 190, and 141.