I find it ironic that "stationery" is often confused with "stationary", because the latter means "not moving", and the whole point is to move it (well, give it) to someone else. If you ever get confused which is which, remember that the one you want has an "e" for envelope, letter, pen and pencils.
Stationery can be in the form of "correspondence cards", which are flat cards. They do not fold. Sort of like a postcard in an envelope, these are great for people who prefer to write brief notes or have small handwriting.
You can also buy sheets. These give you more room and are meant to fold in half. They are a good choice for people with big handwriting! There's also generally room to stamp your name at the top if you want. (Note: You're not supposed to write on the back of an engraved/stamped sheet.)
If you've ever gone looking online for even some simple note cards, you were probably overwhelmed by the choices. Sure you can always go to the mall and find a Papyrus or Hallmark, nothing wrong with that. Papyrus has some really cute stuff and they have printing services too. But if you're looking for something more personal, take a look online. Here are a few good ones:
Remember: If you need help writing, see the How To page.