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)
I would vote for RSS, Twitter, Widgets (such as Google Maps as already suggested), and YouTube. RSS and Twitter give you dynamic content and if it’s for a physical business or establishment, Google Map integration is great if it lets people find directions without having to leave your website, giving the business more “face time” with customers instead of having them visit a 3rd party link to find directions.
The two largest things I think are missing from your list are database integration and security. With lots of websites now having databases in the GB or larger to serve content, having a decent grasp of how to use PHP to read/write information from a database would be a good thing to be exposed to sooner rather than later. In addition, I would also address the need to build secure admin controls and how to handle private information securely (usernames, passwords, email etc.), especially if you are going to be talking about using shopping carts.