The Luna-net video, avaliable in the video section. comes up with this early title screen. In the final there is a ripple effect in the background, here it's simply white.

Secondly is an even earlier 'Choose your Buddy' screen than the ones below. Here only Sonic, Tails and Knuckles are avaliable.

Using Nemesis's PSR uncompressor, we were able to find some very early Character choosing screens. Instead of the 3D model, they would just have the character art become highlighted. This may have been used in prerelease versions where you would be able to play one level of each.

This is the Amy Rose image, click the image for the full sized version.

This is the Big the cat image, click the image for the full sized version.

This is the E-102 Gamma image, click the image for the full sized version.

This is the Knuckles image, click the image for the full sized version.

This is the Sonic image, click the image for the full sized version.

This is the Tails image, click the image for the full sized version.