To my knowledge, this hasn't been suggested before, so I figured I'd put the idea forward.
It's pretty self-explanatory. Much as I love my explosives, I just never use 'em - partly because I play SSP, but also because they're just too messy to begin with. So, I got to thinking - why not make an explosive that only destroys blocks in one direction?
Typically, shaped charges are used in demolitions as well as mining, so my thought was also using it to get through reinforced stone/glass on SMP servers. For a recipe, here's what I have in mind:
X = nothing
C = Clay (balls, blocks, or dust - not sure yet)
T = TNT (Vanilla or industrial - again, not certain, but probably vanilla)
To ensure the blast goes the right way, you could re-orient it using a wrench. I don't know how penetrating the blast should be, but I'd say 3 blocks deep is probably a good ballpark.
So, what do you guys think?