I'm trying to identify what would be the best selling point for a set of articles I'm writing. Should I cover RSS feeds or Facebook/Twitter/YouTube integration into a web site? Or something else? I'm already covering Image galleries, blogs, forums, polls, (and even shopping carts). I apologize if this is too subjective. I just want to know what you are most often requested to create for client websites.
EDIT: Let me put it this way. Say you are learning how to build websites in PHP. You want to get clients as quickly as possible, so which would you learn how to do first: RSS feeds from other sites, or grabbing data from 3rd party sites, like Facebook and Twitter, or integrating YouTube videos? What would likely get you a client first? Something else? (beyond blogs, forums, polls, image galleries, and shopping carts)