Formula 1: Massa's Replacement
Michael Schumacher or Fernando Alonso have certainly been mentioned. Schumacher because he's available and a (retired) legend in his own time. Alonso because he's the most complete driver on the grid and has often been rumored to move to Ferrari, the latest being 2010 so it would make sense if he could be released early from his current contract.
Another benefit of having one of these two drivers is that it will light a fire with Kimi Raikkonen. The Kimster will raise his game as he is faced with a new teammate. He needs motivation.
Robert Kubica is also a possibility if there are performance clauses in his contract with BMW, which has decided to pull out of F1 after this year.
For these reasons I would guess the Ferrari test drivers (Marc Gene, Luca Badoer) or a rookie as a sub would be an unlikely choice to replace Massa. This year's silly season is going to be a media frenzy. We'll see.
I'm hoping for a full and speedy recovery.