HPPA upwards-growing stack: far more logical when one thinks about it, because in an upwards growing stack, the limit of the stack is the available memory, rather than some arbitrary size decided by someone arbitrarily.

SPARC register windows: once one gr0ks them, they are a feature of wonder! The register windows in an UltraSPARC processor effectively provide 256 virtual registers in a processor with only 32 physical ones, giving one increased performance.