The Travel Gnome is a good friend of mine and coworker who always alerts me to reward program promotions and answers all my questions regarding frugal traveling and the vagaries of miles and points programs.
He has done a ton of business travel and frequents places like FlyerTalk and is generally a frugal guy. He carries his change in a sandwich baggie in case you were wondering (I know you weren't)
Most of what I learn from him is applicable if you do a fair amount of traveling, but he has also helped me keep my vacation costs low in general, so even if you don't travel a lot, his tips might come in handy.
Current Rewards Promotions from the Travel Gnome:
Double miles in September and October on Delta (with Amex)
Double points at Marriott October through EOY (with Visa)
Since I mostly fly Delta for work and stay in Marriotts, those are the promotions that are currently on my radar. The promotions assume reward membership and require registration for the particular promotion. Find promotional details on their respective pages.