More than eight: rusps
There are eight-legged animals on Furaha, but they do not walk with their legs in two rows of four legs each, which is mosty what these pages are about. To see a fundamentally different walking patter, visit the page on 'spidrids', also in the 'Walking' section. So, to have a look at animals that do have two rows of four legs, we have to visit Earth, full with spiders...
But a look at other fictional animals is quite revealing: for more info read a post on the subject. Thoats' are animals on Edgar Rice Burrough's Barsoom, or Mars. Many artists wrestled with thoats, forcing them into Earthlike fourlegged shapes. In fact, they tried to do with thoats what the designers of Avatar did with six-legged gaits.
Here is a very nice drawing of a thoat in which the front six legs all move in unison, as if they were a horse's two front legs.
Here is an animation of an eight-legged walker to show that more interesting things can be done with eight-legged gaits. Try to work out what the phase differences are...