Best bang for my buck was the points.com promo. I think I got about 26,000+ AA miles for each of my family members for $5.27 a piece. 100,000+ miles for about $21 or 0.0002 per mile.

Best run of luck has been getting 65,000 delta bonus miles in the last couple months. I started in August with no Delta account at all and now have 70,000+ after one $150 domestic flight and the IC Hotel promo.:

25,000 - IC Promo
1,250 - IC Promo Cert
5,000 - Transfer Bonus from IC Promo Cert
2,000 - IC Hotel Stay Bonus (used free night cert)
10,000 - Fly One Earn Now Bonus
15,000 - Comair Apology miles for a flight I had no problems with over xmas
7,000 - Dash to the Gate Game Bonus
________
65,250 Bonus Miles for very little effort

Total I now have 70,306 - I spent $150 on the IC promo and about $150 a domestic RT. And I didn't have to pay for my hotel stay for the other night for the hotel cert cause someone else picked up the tab. That's just 0.004 per mile.

peace,
~Ben~