I'd like to see Kobayashi in as a replacement. He showed what he can do in a car that he hadn't driven much in the 2009 Toyota. He's popular and is the best driver that comes to mind. I think he'd do the best job.
Kovalainen is another option, albeit safer bet. I do think he's had his chance in F1 now though.
I would also say Heidfeld might be an option if the team in question weren't Lotus.
I still think Valsecchi will get the nod however, what does it say about the team when you fast-track a driver in from outside, it would be incredibly demoralising for Valsecci and show that he was only ever a name in a position to Lotus.