Sometimes I feel like the only one with some memory, although memory it's not really needed when you have wikipedia at hand:
Nvidia 6 series:
6200, 6200 TC2, 6500, 6600 LE, 6600, 6600 GT, 6600 XL, 6800 LE, 6800 XT, 6800, 6800 GTO, 6800 GS, 6800 GT, 6800 Ultra.
Total: 14 cards.
Ati 10 series:
X300 SE, X300, X550 SE, X550, X600 Pro, AIW X600 Pro, X600 XT, X700, X700 Pro, X700 XT, X800 SE, X800 GT128, X800 GT 256, X800 GTO, X800, X800 GTO2, X800 GTO-16, X800 Pro, X800 Pro VIVO, X800 XL, AIW X800 XL, X800 XT, X800 XT VIVO, AIW X800 XT, X800 XT PE, X850 Pro, X850 XT, X850 XT PE.
Total: 28 cards.
Let's see the next generation.
Nvidia 7 series:
7100 GS, 7200 GS, 7300 SE, 7300 LE, 7300 GS, 7300 GT, 7600 GS, 7600 GT, 7600 GT Rev 2, 7800 GS, 7800 GT, 7800 GTX, 7800 GTX 512, 7900 GS, 7900 GT, 7900 GTO, 7900 GTX, 7950 GT, 7950 GX2.
Total: 19 cards.
Ati 11 series:
X1300, X1300 Pro, X1300 XT, X1550 SE, X1550, X1600 Pro, X1600 XT, X1650, X1650 Pro, X1650 GT, X1650 XT, X1800 GTO, X1800 GTO Rev. 2, X1800 XL, AIW X1800 XL, X1800 XT, X1900 GT, X1900 GT Rev. 2, AIW X1900, X1900 CrossFire, X1900 XT, X1900 XTX, X1950 GT, X1950 Pro, X1950 XT, X1950 XTX.
Total: 26 cards.
Nvidia 8 series:
8400 GS, 8500 GT, 8600 GT, 8600 GTS, 8800 GS, 8800 GTS G80, 8800 GT, 8800 GTS G92, 8800 GTX, 8800Ultra.
Total: 10 cards.
But let's add OEM and 9 series since it's based on the same chip (though I could do the same in the above lists and add quite some more).
8600 GS, 9500 GT, 9600 GT, 9800 GT (GTS? Is this one even going to be launched?), 9800 GTX, 9800 GX2
Total: 16 cards.
I could go with Ati series 9 vs. Nvidia series 5 too, but I think I have proven my point with this... (Huh! I didn't make any point? Guess it. lol)
That's what happens when you are in the lead with a strong architecture that can scale well.
And TBH I don't think that's bad, actually I think it's good for the consumer, because you have many cards at different price points with small differences in performance. You can spend as much as you want and you'll get the performance accordingly, you don't have to settle for a slow card (slower than what you want) or spend big $ for a card that is more than what you need. Cough* HD series *cough.