First off, a how-to guide and gallery (including an extensive collection of Escher tessellations) from Tessellations.org.
Lucy Neatby has two tessellated patterns, the Duck Sweater and Fish Wallhanging - a closeup of Lucy's wallhanging is shown here.
The Tessellated Fish Blanket has been a popular subject on the Internets. Hytrevant Knits has an example of the original fish blanket, as designed by Paula Levy and published in Knitter's Magazine 51 (Summer 1998; OOP). April Brokenarrow has reverse engineered a similar pattern; example fish.
Once I started looking for knitted tessellations, it was like learning a new word - you see it everywhere. My Little Fishy is a child's raglan with three bands of two stranded knitted fish. Designed by Marie Grace Smith at The Garter Belt. (This might be stretching the definition a bit, since it has more distinct bands than typically seen in tessellations - but it does satisfy the requirement of interlocking tiles that can be tiled on a plane to infinity.)