Pandora One, Rdio, or Slacker Radio Plus gifts, for the more casual listen-at-work type. Pandora cards are available at some stores, but online is a safer bet. As with Spotify, the gift is subtle, but they'll definitely appreciate it at least twice: once when they activate, once when it almost runs out.
Netflix gift subscriptions are somewhat redundant for people who already know, use, love, and subscribe. I highly recommend it for those who might have Netflix access on one of their devices and not really know about it: on their TV, their Blu-Ray player, or through their kids' Xbox 360, PS3, or even the Wii.
Tricker but still handy last-minute gifts
Forcing them into Amazon Prime is tricky, because you can't give Prime as a gift—not without sneaking into their Amazon account, anyways, which is a bad idea around the holidays. What you can do is get a pre-loaded gift credit card and wrap it around a print-out of an Amazon Prime page, and a note about the free two-day shipping, the streaming movies, and the Kindle "loaners" that are now their standard of living for 13 months (the first trial month is free).
Dropbox, because it will make everything easier. If you know someone is getting a new computer-ish gadget for Christmas, this is just about as good a companion gift as you can get. Like Amazon Prime, there are no gift options (why, Dropbox, why?). But you can do the same pre-loaded credit card incentive, and you can set up Dropbox on their devices and show them how the super-easy link sharing works as part of the gift. And if they have an iPhone or iPad, Dropbox's automatic photo backup service is going to be serious peace of mind.
An actual photo, which is perhaps the best suggestion Ihnatko has in his guide. You are taking and conveniently cloud-saving so many photos these days, but printing out a select image, or a few, can mean so much to your relatives and friends, and it's a real gift they can hold. Bonus points for framing. If you can upload and print out at a Walgreens or CVS or another nearby store before the gift moment, do so. If not, you can buy some photo paper and lose a little ink off your own printer, or give them a Kodak, Snapfish, or other gift certificate that lets them choose the sizing and shipping.