Staying in touch after an interview or when there isn't an opening right now

Very interesting discussion. To kick of I'd say Twitter (sorry for stating the obvious), however you can't force anyone to follow you and more importantly read what you're tweeting ... What might help as well - and this is a "method" that without the real intention to really, has connected me to a few people (and might thus work to stay in the minds of "companies" too) - is to get the word out on the things these companies/employers are doing or working on which you really dig. If they're on top of things, they may well notice the support, which in the long run may benefit you as well I think ... (Needless to say, it's important to keep it real ...)

After the initial follow up, if you see any relevant news articles or posts about the company/industry, sending them along will show that you're interested in the company, but not just emailing constant check ins. This doesn't have to be an every day or every week thing, but sending really topical information as a "Saw this and thought of you" approach is a great way to show off your character and your interest in the company.

Keep the interviewer as your direct contact until they point you to someone else. Like @kmaverick said, showing your character and interest is clutch. When you follow-up, make reading your email worth their time. Also, don't hesitate to share any new accomplishments that may have come your way - It's okay to exude confidence, just don't go overboard. Be genuine.

This is a great question. Depending on the size of the company, or how frequently they use social media, I would make sure to comment on any blogs, or twitter feeds and send them information they may find relevant. Become someone they can rely on for useful info, and they will remember you the next time they have a position. It's also a great way to make contacts and get a feel for the company.

This is hinted at above, but I'll say it succinctly: The best way to stay in contact with your prospective future employer is to use the check-in as an opportunity to deliver value to them. Whether that's forwarding things you see on the web (but be smart - they've seen the businessweek article on their company) or whether that's bringing them something that could be useful to them. In the specific case of venture capital it's often bringing an interesting company to a given investor's attention, but there are tons of analogs in other businesses where you can either help them make a connection or bring something to their attention that helps them do their job better. Do that, consistently, and they'll absolutely remember you.

In the design world, it's always nice to receive actual snail mail note to follow up. Perhaps you include printed work samples or direct them to something interesting that may relate to a topic discussed during the interview. It's also good to remind them where they can check online to keep updated on your professional work/status. It might be a good idea to send a beautifully designed postcard/email with a personalized note every so often with something new to remind them of you/your work.

During the informational interview it is a good idea to ask the person about what they would like to know more about. What are their areas of learning, curiosity...?

That way, you can be aware of the area that they are eager to hear news about -- and then perhaps offer to send them relevant items in that area.

Or if you are not confident about picking up this material, then perhaps don't promise anything (you initial questions would anyway be part of your interest in the person behind the job) , and surprise them if something shows up.

Some people would be happy to hear how you get on in your job search. Not everyone, but I think these things very much depend on the spirit in which they are executed.

One person I know would send a very genuine and detailed overview of his jobsearch to his contacts. It felt like a newsletter. His character really came through and because it was well-composed and so full the initiatives he had made, I suspect it worked to align people to his quest. it certainly did with me.

in terms of keeping the contact -- you could actually ask the person -- "are there other people you would recommend me to in the organisation?" Or if there is someone you are aware of -- just let them know - "I would love to speak to Jenny Pearson too about x,y,z. Would you introduce me?"

If you have built trust with them then they will likely be glad to facilitate the intro.

It really depends on many factors. Acting transparently (being open about who else you would like to make contact with) often avoids future problems and if people are on board your own quest for a great job then they will generally not want to act as gatekeeper for people/information that could support your quest.

Of course if the situtation is sensitive and there is a valid reason not to initiate contact with someone else, then respect that set up.