PTR
Striker
At least the new regs were created specifically to allow close racing. For the first time, the FIA have a real R&D team working on it, rather than just guessing like they did before.the problem may be though that one team see's an edge that gives them a head shoulders advantage (ie. brawn 09)...
Mind, the last regs were OBVIOUSLY stupid from the get-go. Bigger cars, bigger wings to be faster - that was always going to make it harder to overtake.
Grippier tyres and some ground effect to keep the speeds up, and move the balance away from too much aero should make a huge difference.