If I were to look at free agency I would take Jeff Garcia.
For a young, rebuilding team? I think KC wants a franchise type QB or at least in Thigpen, a young QB who, if he continues to develop can be built around. Garcia will be 40 by the end of next year. I don't see him fitting in with a young team. Especially if he wants to be a starter. Minnesota might be a good fit for him since they're in "win now" mode.
On paper, I could actually see him being a good fit for Dallas since he and Romo have a similar style of play but there's no way he would reunite with TO.
If Cassel is dealt by New England(which I think is a very distinct possibility since I still can't believe they'd be willing to pay him $14M), that would be an ideal spot for Garcia to possibly land. Brady's going to need time and Bellichick has had guys like Testaverde, Flutie, etc. as insurance in the past. If Garcia take any kind of a backup role, I think New England would be a place he would do it.