I'm only listing the ones which come to mind immediately. There are others (part...

I'm only listing the ones which come to mind immediately. There are others (particularly apps with one-off up-front payments) which I don't use regularly and turned out not to be important to me.

One-off (paid or freemium):

  Pleco (Chinese dictionary with paid flashcard functionality)
  Groundwire (SIP client for iOS, including Push notifications)
  GoodReader (PDF reader and organizer for iOS)
  Pushover (trigger iOS push notifications from email, IFTTT etc.)
  MindNode (iOS mind-mapping)
  BubbleUPnp (Android DLNA server)
  SnappyCam Pro (iOS camera)
  Cycloramic Pro (iOS camera)

Regular payments:

  Pandora (streaming radio)
  Several different virtual servers (for web apps and VPN)
  Newsblur (RSS reader)
  DIDLogic (monthly fee to get an inbound local phone number)
  The Economist (print subscription includes online/app access)

Usage-based fees:

  Rebtel (outbound phone calls)
  DIDLogic (outbound phone calls)