I just finished a pretty solid interview and I want to make sure I leave a lasting impression. I've heard some people say something handwritten is a really nice touch, but isn't "snail mail" dead?
Both! I like to send "thank you" email as soon as possible after interviews so that the interviewer knows that I'm eager and on top of things. Then, I like to drop a handwritten note in the mail the next day as a "cherry on top".
You don't really need the handwritten note, but you should at least send the email. Surprisingly few people send a thank you note after an interview, and it will really help you stand out. Ask for your interviewer's business card on the way out the door, and if you forget, you can try to Google the person's work email or potentially ask the recruiting coordinator for the interviewer's email so that you can say thank you.
I think email is totally fine. The more instantaneous the better. A nice handwritten letter can wow your recruiter, but do you really have time to wait in line at the post office? ;)
I vote for email, primarily because of speed. Mail will take a few days and the interviewer may have already made their mind up after they've received it. You want them to receive the message right away.
Email is really the only pragmatic way. A hand written note is a nice thought - but the reality is it gets lost at many larger companies in the "corporate mail". It would be best to send an email immediately (I mean within the hour) or within 24 hours. It shows a higher level of interest on your part.