the lads at Bell Labs thought that # should have a more distinctive name than the various pound, hash, (cross)hatch, sharp, etc. and came up with octothorpe (from its eight points and some guy named Thorpe). it hasn't caught on.

the paragraph mark ĥ is called a 'pilcrow'
the squiggle under a ç is a 'cedilla' (as in façade)
@ is more formally called the 'commercial at'
µ is the 'micron'
other names for the slash (/) are 'virgule' and 'solidus'
the backslash (\) is, of course, the 'reverse solidus'
and, finally, an old word for the ? mark is 'eroteme' (ER uh teem)