I have an OA Non-Immigrant visa (M entries) issued on 7 Oct. 2008, with an 'enter before' date of October 6 2009. So if I leave and re-enter Thailand, I get another 'one year' maximum stay in the kingdom.

I entered Thailand on 30 Oct. 2008, with an 'until' date of 29 Oct. 2009. My date of departure of Thailand was 22 April. 2009.

Which date governs my latest re-entry date to obtain another one year stay, (1) the 'enter before' date of 6 Oct. 2009 on my visa, or (2) the 29 Oct. 2009 'until date' showing on my admitted stamp connected to my visa?

Thanks.

You must enter before Oct 6 to use your visa - if you do enter before that date you will get a one year permitted to stay stamp from the day you enter. Any travel with a return after Oct 5 will require a re-entry permit prior to leaving to keep you current stay alive.

Yes. October 6th is the magic date. Enter before that date and get another 12 months.