Thought I would start this thread and maybe it will become a sticky.
1. 2007-2012 MS3 rear motor mount (OEM or aftermarket. Helps with wheel-hop and provides a more "connected" feel between the chassis and drivetrain. Better shifts as well.). You can order at local Mazda Dealership, the part number is : BBN-39-040 price is right around $40
1.5) Factory Mazda bolt: 9YA0-2A-226A will cost about $9
2. 2007-2012 MS3 springs (2010-2012 recommended). Excellent results, but if you want an even front to rear ride height, you should cut 1/2 to 1 coil from the bottom of the front springs.
3. MK2 headers such as F2 and FSwerks fit with out issue, just get the longer flex pipe when ordering.
4. 2010+ MS3 struts (with modification) and rear shocks. See this thread: Suspension fix - no more front end clunk
As we add parts, I will add to the list. I know that amoosenamedhank is working on putting MS3 swaybars on the MK3 Focus as well...