Two additional things that seem to work with more than acceptable success:
First, one of several solid escapes from the body triangle from Bill Coopers Escapes DVD:
Hook their leg like how In the video drew linked, the motion he says you can try to do at 0:33, take your leg over their shin and across their foot, turn towards the opponents other knee(the one w/ white sleeve in this vids case), look towards them (passionately into their eyes, if possible) then push down on their knee(white sleeved knee). This is a pretty solid ankle lock...
[edit: this seems to be the technique AKRhino described above as well, I didn't see his post until after I posted]
Second, everyone always says 'dont cross your legs/hooks when you have someones back', and everyone knows why... So note what happens when he does at 45-47 to push the leg in, once he does that, the opponents legs are fully crossed, and you can now figure four ontop of them for the traditional footflex/slice attack on a person who's legs are crossed...
Most of the other escapes I use from this position are from the bill cooper dvd, are based on the movement done at 45-47 secs in the video drew linked, but my favorite is the one based on the movement at 0:33 if you can hook the foot...