"Geeing whiz" is a colloquial expression that conveys surprise or astonishment. As with any colloquial expression, there are several synonyms that you can use in place of "geeing whiz" if you want to mix things up a bit. These synonyms include "wow," "amazing," "holy cow," "unbelievable," "jeez," "oh my goodness," "golly," "goodness gracious," "holy smokes," and "holy mackerel." Each of these expressions conveys a sense of wonderment, excitement, or disbelief, and you can use them interchangeably with "geeing whiz" depending on the context and your personal preference.