Colombia - Isn't the current government pretty right-wing? But a lot of people are citing it, so...
Albania - Haha, no. Eastern Europe has never been gay-friendly.
Luxembourg - Good shot of it, IIRC. All three gay couples will be able to marry soon.
Vietnam - From what I've heard, East Asia has never cared much either way about homosexuality. Possibly.
Cuba - Not impossible, but the PCC has been pretty homophobic in the past.
Taiwan - See Vietnam, but more democratic.
Finland - Yeah, this is probably coming soon.
So in order from most to least likely:
Finland
Luxembourg
Colombia
Taiwan
Vietnam
Cuba
Albania
Colombia: A gay marriage will take place in Colombia on July 24th, in conjunction with a court order. It remains unclear though if gay marriage will become available on demand at this point or if every gay marriage will require an individual court order.
Albania: Both major parties are for gay marriage. They would have legalized it before but the opposition (now the government) was boycotting because of claimed election fraud, thus denying a quorum for amending existing laws.
Luxembourg: The leadership of all main parties is for it but the issue lost on a free vote. A new parliament might be different though.
Vietnam: There's been talk coming out of the judicial branch.
Cuba: USED to be very homophobic. Not any more. Raul's daughter is head of a gay rights organization. The government pays for transsexuals to get realignment surgery. I'm actually surprised they did that before they did gay marriage.
Taiwan: Again, rumblings from the judicial branch.
Finland: What everyone else said.