So yeah...the title describes it pretty well. Weird/uncommon languages are welcome too. (Not sure if Brainf*ck counts...)
Flat Assembler...
nasm
NASM isn't really a language, more of a format for Intel ASM. But yeah, I definitely prefer that over MASM and TASM. Haven't tried YASM, though.
RedCode
I see you play Core Wars, then?