I bought a strip of them a few years ago about 25mm disks with an adhesive back I think they run at about 40p each.
If you download NFC Tool for Android you'll see what you can do with them but the brief list is:
Text, URL, Social Network links (URLs again), Create a prefilled E-mail, Add contact details, Add Location Details, Add Wifi Details.
I don't use them overly regularly but I do have one by the front door so if gusts want to get on my Wifi they just tap their phones and it loads them up. I also made a leather key fob for someone with their contact details so they could use that instead of a business card.
You can lock them from being edited too, I've used this on a few bikes before with my details in, you just have to put the tag where it won't get removed easily, the bottom bracket is normally a good place.
You can get various apps where you can program your phone when it taps a tag, if you switch your work phone to silent as you enter the house you could put a tag by the door and tap it on the way in.
In terms of communicating you've got a solid state chip which stores the information on. As you approach it with the phone the phone generates the power for the chip to work (similar to wireless charging). They last for years and can be easily reused elsewhere.