Notice the benchmarks. The ATi cards fall behind the nVidia counterparts, mainly due to the 16 pipes in all cards.
X1800XT will feature 512MB of RAM @ 600/1400 and 16 pipes - $599 X1800XL will feature 512MB of RAM @ 550/1250 and 16 pipes - $499 X1800Pro will feature 256MB of RAM @ 500/1000 and 16 pipes - $449 X1800LE will feature 256MB of RAM @ 450/900 and 12 pipes - $349
I believe all of them feature DDR3 RAM. There is also a X1600 lineup to replace the X600 series and a X1300 lineup to replace the X300 series.