Besides Siri, are there any applications which integrate with OmniFocus.
For example, in my RSS reader or Twitter client, I would love to send items I wish to read later to OmniFocus instead of Instapaper or Readability.
There's a list at http://forums.omnigroup.com/showthread.php?t=18931. Not a lot, I'm afraid. There's an API available but I guess there's not enough consumer demand for that feature.
For other apps, you might be able to make use of the "Send-To-Omnifocus" feature. From your RSS or Twitter app, forward the item by email to firstname.lastname@example.org.
You will get an automated reply containing a link: click the link and an Omnifocus item will be created.