The Canon 600D is the latest in the range of affordable DSLR cameras that started with the Canon 300D back in 2003.
Compared to previous generations of this range it includes a rotating LCD screen, external flash control, HD video crop modes as well as the same 18Mp sensor in the Canon 550D/Canon 60D and Canon 7D.
The only reason I can see that you would want to buy a Canon 60D or Canon 7D instead of a 600D would be for increased frame rate or a more robust body. Otherwise the Canon 600D covers pretty much all the requirements you would have.
I think the following features over the Canon 550D are for me well worth the upgrade. Overall the deal was cash neutral as the price for the Canon 550D covered the cost of the Canon 600D.
1) Rotating LCD screen - definitely a real bonus for shooting video and Live view.
2) Video crop mode - far more flexible feature on Canon 600D compared to the Canon 550D
3) Wireless flash control built in - will be very useful and save needing to use the Canon ST-E2
Other features that are available on the Canon 60D such as faster frame rate, higher Raw buffer are not things that I would need. The additional focus points that the Canon 60D offers compared to the Canon 600D/Canon 550D are of no use to me as I primarily only use the central focus point anyway.
