what's the difference in these cards?

[StingElectra]

So what's the difference between the gtx 660 and the gtx 660 ti because I noticed the ti is more expensive

 

[jpoos]

main difference: increased number of shaders. 960 in 660, 1344 in 660ti.
http://en.wikipedia.org/wiki/GeForce_600_Series specs for the whole 600 series