Keychains you can squish! Here are classic style Sonic & Eggman squeeze keychains. They're fully 3D figures, but made of a soft, colored foam. The keychain part fits in a loop at the top, and hangs down behind them. They're a bit big for a keychain you'd want to carry around (won't fit in most pockets) but they're still fun to collect. They're simply bubble-carded for retail sale. The card has a nice Green Hill Zone background with the familiar palms and flowers, for nice effect. These appeared in Australia Stores (Including Gametraders) in March 2011. These cost about 10 AU Dollars each.
A classic set wouldn't be complete without classic Knuckles, so here he is in both squeeze-toy & squeeze-keychain form. He's pretty on-model in both cases, though the toy's feet may be a little small, while the crescent of white for the chest is a little low. Why he wasn't pictured/on the set from the start is unknown, but at least now in 2011 he's available. This photo also gives you an idea of the size of the two squeeze items as compared to eachother.
Here's the full set of the classic squeeze keychain figures. They're not to scale, though Eggman is a little larger than everybody else. They're classically cute & fun, with limbs posed close to the body to minimize breakage possibility.