It will be the Radeon X1900 (R580), which will be pin-to-pin compatible with the X1800XT PCB.
Its competitor will be nVidia Geforce G71, a new gen 90nm core. Seems like the Q1 of next year will be an interesting year as the war BTW ATI & nVidia heats up.Unfortunately the sources also claim graphics cards will hit a new record price. It's expected prices of ultra high-end graphics cards will rise to $1,000 by 2007..
Furthermore, a cheaper version of ATI Radeon X1300, RV505, will also be released Q1 of 2006 to fight against nVidia G72. RV505 is about the same as RV515, the only difference would be the 80nm process which makes it even cheaper. Same idea as RV380 vs RV370 of last gen.