Pretty broad question - but two things to consider - 1) buying US Savings bonds with those credit cards; and 2) changing Long distance service a lot to earn miles. This isn't as easy as it used to be, but there are still a lot of miles out there to be had.

I'm sure others will have suggestions - I also like this site, done by a FlyerTalker:

http://home.earthlink.net/~pgary/TravelFrame.html