In addition to a regular NOP, the Motorola 6809 (and possibly other 6800-series processors) has a BRN instruction: branch never. It's the opposite of BRA (branch always): it takes an 8-bit offset and ignores it, effectively making it a two-byte NOP.
On PIC microcontrollers, it's common to use a "goto $+1" instruction as a two-cycle NOP to save an instruction word (every word counts when you only have 256 words of ROM and 32 bytes of RAM). It just branches to the next instruction.
I remember that from the 6811s we programmed in school. BRN also takes more cycles to complete than a standard NOP (or 2 NOPs) since it performs some branching calculations before it ends up doing nothing.
