I'm currently on a tourist visa; 60 days + 30 extension. I'd like to leave the country at the 45 day mark without losing the rest of the days. In other words, when I come back I will have 15 days left on the tourist visa (plus the 30 day extension). Is there some sort of special stamp I can buy at the airport which will allow me to do this? I thought I read about it before.

NO, not any more (the airport office closes permanently today)

But you can buy a re-entry permit at any immigration office, 1000Baht for a single re-entry (take a passport photo with you), this will protect your current exit date (it will not 'save' days as such).

If your return will be after your current stamp expires, get the extension before you leave (and before you get the re-entry permit) you can apply for the 30 day extension any time during the 60 days stamp.

Edited January 14, 200917 yr by Crossy

You need to get a Re-Entry Permit from immigration (recommended) or at the airport immediately before departure. You need to fill out the application form, have pictures with you, passport photocopies and pay 1,000 THB for a single re-entry.This will only work if you return before your Admitted Until (permission to stay) date, if you need more time outside the country then you need to get the 30 day extension before leaving.

Edited January 14, 200917 yr by InterestedObserver

I'm currently on a tourist visa; 60 days + 30 extension. I'd like to leave the country at the 45 day mark without losing the rest of the days. In other words, when I come back I will have 15 days left on the tourist visa (plus the 30 day extension). Is there some sort of special stamp I can buy at the airport which will allow me to do this? I thought I read about it before.

No. You are thinking of a Re Entry Permit. 1,000 Baht.

This keeps your current permision to stay date alive. It does not freeze anything. So if you left for 15 days it would be expired when you return. As Crossy said, it would work if you got the extension first. It all depends on how long you are staying away.

Also we have reports that the office at BKK Airport is closing on 15th Jan.