Thanks to this simple but powerful API from Google, you can now simply send the URL to an XML feed, and receive that data back in nicely formatted JSON! The syntax is extremely simple and all you need is a Google Developer Key (Update: this is actually optional, but preferred by Google).
I will use my blog as an example of using this API. If you load my blog feed now, you will notice I use Feed burner (another Google product, see a pattern emerging?). As far as I know, Feed burner doesn't support feeds, so that's why it's a perfect example of when to use this API.
The above url will load my blog and display only 10 results, returning the results in JSON format. You can also provide a callback and many other filters, but those you can decide on yourself! Full documentation can be found over at JSON Developer's Guide.