I would love to nominate the following, because these are my memories of RadioSEGA ever since the dawn of my registration date:

OutRun 2 - Night Flight;
Daytona USA 2 - I Can Do It;
SEGA Rally Championship - My Dear Friend, Rally;
Bayonetta - After Burner (Infinite Climax Mix);
Jet Set Radio Future - Aisle 10;
Streets of Rage 2 - Expander;

And finally...

Sonic & All-Stars Racing Transformed - Seasonal Shrines (Idated/Japonesque - Shinobi III).

These were my all time favourites, whether it was when requesting them on the 24/7 feed or in the live shows, and they will be forever a memory of how I learned so much with RadioSEGA. :D