LifeMiles has been offering 100% bonus for purchased miles couple of times a year. What makes this offer exciting is the fact that the airline is now a full member of Star Alliance and you can use the purchased miles for awards on all Star Alliance carriers. LifeMiles just sent an email regarding their latest offer.
You can buy up to 75000 miles for $2250 that is doubled to total of 150K miles. The price of a purchased mile is reasonable 1.5 cents. This offer is valid from September 3 to September 28, 2012. You can access this offer here.
You can use the purchased miles to do cash + miles awards even further extending the number of miles purchased.
AviancaTaca has very good frequent flier program for Star Alliance awards. Even if you are not planning to fly the airline in question it can make sense to buy the miles if you use them for international business and first class awards.