nv40: 6800, 6800GT/Ultra, 16pipes(4 disabled for regular), AGP
nv41: native 12 pipe 6800, native pci-E
nv42: mainstream, probably called 6200, AGP
nv43: 6600/6600GT, native pci-E
nv44: mainstream, probably pcx6200, native pci-E
nv45: nv40 with PCI-E bridge
nv46-49 for future offerings.
nv5x: next generation
r400: delayed, renamed r500
rv410: 110nm version of rv420, will compete with 6600/6600GT, native pci-E
r420: X800 pro/XT
rv420: 130nm, cancelled
r423: r420 w/native pci-E
r430: 110nm version of r420
ATI's x600 is rv380 and is just a 9600(rv350/360) with pci-E.