My roommate bought this planner recently from Barnes and Noble. It is from the Silver Lining brand, although I couldn't find the illustrator's name. I thought this whimsical cover was cute, and appropriate for a casual book such as a planner.
The elephants are fun to look at because they have different patterns and colors on them. I like how the elephants are outlined, and how everything is simple line work, pretty much like a doodle. The rounded corners on the cover even mimic this curvy line work. The lines are flat, yet the different colors and patterns help give each elephant more of a dimension, which I think helps make them more interesting to look at. Also, the confetti and tear drop shapes make it seem like a parade, which adds energy to the design.
However, even though the elephants each have a different design, they are all linked by common colors and style. The color scheme is nice and calm, and the wire binding even fits in with this scheme. The greens and purples are calm yet still interesting. The composition is also helpful--some of the elephants fit together like puzzle pieces while others overlap. This also adds dimension.
Even though these are fairly simple drawings, there is a lot of variety in color and texture so that the book does not become boring to look at (especially if you use a planner every day for a year).