560 Ti is a high end card by all means (this is how it is labeled everywhere).
Its one of the best deals when it comes performance for buck, and still a powerfull card.
Sure, you might not be able to max all games out there, but by a relativly small margin.
While newer GPUs are definitly better, those are not needed yet since the graphics on games is hardly progresing latly.
Among the most demanding games, metro 2033 (can run full hd high settings), Witcher 2 (can run full hd High settings), Battlefield 3 (can run full hd ultra settings),
etc.
The problem is that if you go higher (for example a GTX 580, since 570 is almost same as 560 Ti when you overclock), the price goes up so much, that you are getting ripped off.