Here's the A7N8X line:
A7N8X-Deluxe - Soundstorm audio (hardware audio ob), dual LAN, Dual channel DDR400 memory, Serial ATA, 6 USB 2.0, Firewire (IEEE1394), Dolby Digital (SPDIF output). Top of the line board, and very nice.
A7N8X - Software (Realtek) audio, onboard LAN, USB 2.0, dual channel DDR400. Same performance as the Deluxe, but lacks most of the extras.
A7N8X-X - Software (Realtek) audio, onboard LAN, USB 2.0, single channel DDR400. Same as above, but lacks Dual channel memory mode. (This is a *very* minor performance reduction.) The board also has no extras, just a floppy ribbon, 80 pin IDE ribbon, and backpanel (ATX) plate to fit the board.
There's also some talk about a A7N8X-E, which is supposedly the same as the Deluxe, but with Gigibit ethernet. I haven't seen this board yet.
The A7N8X-VM is also available, which is a microATX board with onboard GeForce 4 MX graphics.