Here's a new tutorial I put together featuring two different open gaurd triangles:
Open Guard Triangles: a Brief BJJ Tutorial
Check it out and let me know what you think!
In for later 
goaTTT
It's later now.
" From double sleeve control, you're going to opt for cross-sleeve control, meaning your right hand will eventually control their right sleeve. Now weave your right leg under their arm, all the way across their stomach to the other side of their body. You can grab the pants with your free left hand here, preventing them from rotating. Now you have a really nice shoulder lock attack. "
I think in this paragraph you mean to say weave your left leg under, am I correct?
Do you have any tips on breaking their grips on your belt after they commit to the double unders? I always end up in a dogfight in that position.
CraftyHobo - It's later now.
" From double sleeve control, you're going to opt for cross-sleeve control, meaning your right hand will eventually control their right sleeve. Now weave your right leg under their arm, all the way across their stomach to the other side of their body. You can grab the pants with your free left hand here, preventing them from rotating. Now you have a really nice shoulder lock attack. "
I think in this paragraph you mean to say weave your left leg under, am I correct?
Do you have any tips on breaking their grips on your belt after they commit to the double unders? I always end up in a dogfight in that position.
Thanks for the heads up on the typo! Fixed.
When people grab my belt from double unders, I actually look at it as an opportunity. Figure their hands are essentially glued in place, and I can work around that. In order to create space, I really like pushing the head to one side, then scooping the near arm for a crucifix attack (you have to weave your leg over their arm). There's also the classic "arm pry" triangle set up from double unders, which (again) requires moving their head to the side. Hope this gives you at least a starting point!
TTT