You should check the following websites regularly:

http://www.freefrequentflyermiles.com/index.htm
http://www.webflyer.com/blog/
http://www.mileageworkshop.com/

Also, think about a subscription to Inside Flyer magazine.

Finally, make sure you sign up for the relevant idine programs--another example of racking up lots of points with little or no modification of your normal spending patterns!