One such composition is ultra/bling/infestor, inevitably with mass lings thrown in the mix to help soak up the surplus of minerals. The thing is, while banelings are not cost effective against protoss armor, they can still wipe it out if you have enough of them, something roach/hydra/corruptor will never do. When you are in a 200/200 vs. 200/200 fight, and you are piling up thousands of minerals and gas - you don't necessarily need to be cost effective, it would be nice to just completely obliterate your opponent's army and still have a good portion of your own left standing. As long as a big enough portion of your army is leftover, he will never be able to reinforce fast enough to defend his expos and tech buildings after his first deathball is destroyed - something this composition makes possible. It is really pretty straight forward, fungal everything which will remove most of the shields and keep the army in place, rush in with baneling/ultra, ultras will break through any FFs and finish off whatever the banelings don't explode. If they have stargate units in the mix (they usually do) these can be NP'd but mostly ignored. The zerg ground army will roll over the toss ground army and as long as you plan ahead and throw down a hydra den when you are 200/200 you can reinforce with tons of hydra to deal with the leftover stargate units.
Mothership can make it difficult as well, whenever I've gone up against mothership with this build I tried to NP it but still didn't have enough detection to win leaving most of his ground army intact, I'm not sure yet if I just need more detection or if it just doesn't work against mothership. It does seem like with enough detection the zerg ground army will be able to still roll over the toss ground army while ignoring the mothership. I've also been practicing this with a sort of tunnel vision to work on the build, so I'm not exactly looking for openings to punish them while they are teching too hard.
As I have been practicing this on the diamond ladder and the main problem with the build by far is actually surviving to a max army situation. Since it is ladder sometimes toss will just sit back and let me max out, thinking they will be able to max out their deathball and easily win - this turns into an easy win for my deathball. The real bitch is surviving a 5 or 6 gate attack, and even heavy sentry "pressure" can be game ending when you are trying to defend with ling/bane. Regardless it is still something I am working on because I think it has potential. I have been winning some games and losing several, but I still have plenty of room for improvement with my execution and timings.
If I can just find a good way to hold off that gateway pressure I think this will be a solid build. I need to find out if it is viable to get infestors out in time, find the right time to take a 3rd, maybe even defend with roaches and and then switch to bane later on - I've only been trying to defend with ling/bane to make use of my upgrade path. Also I need to work out the exact timing for a macro hatch and maybe add a second macro hatch after taking a 3rd. Sometimes I lose to gateway pressure but I am sitting on 2k minerals and no larva.
Comments from my opponents have been humorous, everything ranging "wtf zerg is so op" as I roll over their deathball and "what league are you in noob?" as I helplessly try to defend 6 gate with ling/bling. It's also hilarious to see shattered temple completely covered in creep with the protoss death ball trapped in the middle with MASS banes circling around waiting for the ultras to hatch. Once you get enough banes they are terrified to step away from the FFs.
Either way, success or fail, it is really a blast to play SC2 in this way, actually trying new things and experimenting with the game instead of focusing on the "right" way to play. I highly recommend it.