- Tony's comment about the roulette wheel being based on the same principal as the solar system (notice how the ball falls towards the "sun" when it's rotational momentum -- i.e. life -- ends);
- Tony's "I get it!" moment when the desert sun flared at him, coupled with his infatuation with its light, as he later tried to explain to the guys at the pork store;
- his related comment to Melfi that "there's something else out there";
- Tony's wistful, yearning expression near the end of MIA when he looked up at the sun and heard birds/ducks call as they flew across the sky;
- the metaphor of Tony as a "blue comet" (as billymac so intelligently explored http://thechaselounge.net/showthread.php?t=1857) whose unusual orbit can take it perilously close to the sun or permanently eject it from the solar system;
- the fact that the conference Tony was attending in his coma had a fair amount of space/celestial symbolism -- satellite icons, air force colonels, Carm's "you should not go on to Houston", Finnerty's occupation as a "solar heating salesman", etc.;
- the marked contrast between Tony seeing dead family members and a gradual fade to white at the Inn at the Oaks and the sudden cut to black that ended the series;
- the central fear, revealed in his very first therapy session, that was fueling Tony's panic attacks and depression: fear of losing his family.
I'm absolutely convinced that the following things are connected:
Tony, his spirits crushed after b-lining to the fridge first thing in the morning: "Who ate the last piece of cake?"