Graphics card upgrade for 24" 2.8Ghz Intel Core 2 Duo iMac

Hi,

I have a 24" 2.8Ghz Intel Core 2 Duo, that I bought in November 2007, which has the ATI,Radeon HD2600 graphics card.

I notice matthewfray mention the 8800 GS in another post, though this is ridiculously expensive..!!

Is there a GeForce alternative that isn't branded 'Apple Original Part' so as to bump up the price..

All the GeForce cards I am finding aren't internal fitted, they're basically for towers..!

Any help pointing me in the right direction would be great..

Thanks..Az