There are online services, and there are online services. Amazon Prime is the latter. And while subscriptions are generally bad things to buy people as presents — I have a general phobia of committing to anything, quadruply so if somebody is foisting it upon me, like most twenty-something males — Amazon Prime is the killerest of killer apps.
A year of Amazon Prime provides, in order of awesomeness: free two-day shipping of basically anything on the site sold by Amazon (TVs, toilet paper, 1500-pound gun safes), one-day shipping for $4, unlimited access to Amazon Prime Instant Video (which isn't as good as Netflix yet, but it gets better every day and is already pretty decent) and free book lending through Kindle devices. And it can be shared it with family members who don't even live in the same state.
Free two-day shipping sounds like a perk, a trifle, a distraction even — but it is transformational to the experience of being a consumer. The psychological barrier between wanting something and purchasing it becomes thin on a molecular scale as your brain begins to process that almost anything you desire simply appears at your doorstep; this is particularly true if you have Amazon's app on your phone and there Amazon does not collect sales tax in your state. It almost feels like a superpower. So it's hard not to abuse Prime eventually. Amazon's probably eaten at least a thousand dollars in shipping costs on my behalf over the last couple of years as a result.
The caveat: Buying someone else a Prime account for a year — which costs $80 — as a gift is not easy. Amazon gift cards can't be used for Prime. There is no mechanism for giving someone a year of Prime. You'll need to create an account for them, perhaps, or procure their login information or hand over your credit card. Not exactly the most fun way to give a gift. But whoever you give it to will assure you that it was worth the trouble.