Sonic & Tails 1 also had a poster.
This Game Gear game poster has a fun feel with colorful icons of enemies & tiny screen shots scattered around the striped/rays background. It has a nice eye-catching large art of Sonic & Tails jumping/looking fun. The game's logo is at the bottom, along with more screen shots so you can tell a bit of what the game will be like.
The whole bottom part is taken up by white space with a full year of calander on it. Notice one little enemy badnick has made it under the calander. This helps keep the poster useful, even after the game is released. However, with the nice art & cute item placement, it remains a cool decoration item anyway.