Define "cool"...
Layering explosives like C4, TNT, NITR, etc. can make some interesting ones, if you're looking for non-nuclear, but they're relatively weak.
Layering PLUT, surrounding it with TTAN and putting some pressure can be very powerful.
Using BCLN (THDR) can be devastating.
Or if you're going purely for looks, burning BCOL with gravity disabled is cool
Use layered compressed DEUT or SNOW(SING).