What about a blog? I agree Skype is great too.
Ours are all several thousand kms away, and we use all of the above. Though neither set 'do' facebook and that's great with me cos I'm not a fan.
DH's parents refuse to buy a computer to get updates so they just have to wait until I can print an mail photos. We ring each set weekly and invariably there's not much to say but at least the contact is there.
When we lived closer (like 600kms away) we used to make a trip at least every couple of months or encourage someone to come down to us. Funny though how it was always us making the effort. Now that's it's an exxie trip and difficult with youngsters it will sadly be much less often like once a year.