I would say the closest current day cards to the GTX 260's performance would be the Radeon HD 7750 and the GTX 650. The GTX 650 would be a bit faster than both those cards, and the GTX 260 would be a bit faster than the Radeon HD 7750. The performance difference between the GTX 650 and the Radeon HD 7750 is not very large though. The GTX 650 maybe better by 10%, and I am not talking about the more powerful GTX 650 Ti or GTX 650 Ti Boost versions.
What is your budget?