Some personal favorites were the IHG Priceless Surprises. I was in India at the time and was able to fill out postcards to do the max # of entries for about $27. I netted $150 of VGCs and about 200k points if I recall correctly. A couple months before that there was a different IHG promo, I stayed 2 weeks in Wakkanai Japan at $7 a night and ended up with 70k points.

And of course Eurobonus millionaire! I can say this now, I just got my mil today. Really fun promo!!