Well, it's supposed to be the Geforce FX 5900, but the FX cards were bad, don't get one of them, 9800 pro is the best bang for the buck card there is right now, if you can't afford one of the new ones 9800 pro is the way to go.
There is nothing equivalent to the 9800 Pro. The closest would be the 5900, but its not a perfect equivalent. The more shaders in a game, the more the 5900 will be bogged down. The 9800 Pro won't have this problem.
There is no card equal to the 9800Pro 128MB 256Bit. There are a few cards above it but for more money. The 5900U will perform similar to it in older games but the new games it does drop quite a bit. Even in HL2 in full precision, the 5900U will perform about the same as a 9600Pro.
9800XT, 6800, X800SE would be the closest but they cost more.