I'm a huge fan of Giftcardmart.com as well. It's true they openly embrace MSing - I discuss latest credit card deals with them frequently. They sometimes send out good deals by email too.

They're the small guys, so they don't accept everything, but their rates are often competitive.

I usually go Giftcardmart.com > SaveYa > Raise > Cardpool. I used to use Giftcardzen but Cardpool's HQ is closer to me (literally a block away) so shipping and getting paid are much faster. I love GCZen but don't like how it takes them a bit of time to verify your cards before they accept the order.