RSS Mixer is a simple application for mixing multiple RSS feeds together into one feed. Interestingly, you can then take the new feed and output a custom feed for your iPhone, an Apple Widget, snaggable widget or feed reader.
I created a feed mashup for TECH cocktail and Somewhat Frank here. Of course you could give myAOL Favorites feed reader if you create a folder add a bunch of feeds and click the green "Mix & Share" button.